485BPOS

As filed with the Securities and Exchange Commission on May 22, 2012

Securities Act Registration No. 2-34223

Investment Company Act File No. 811-1829

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-1A

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

Post-Effective Amendment No. 94

and

REGISTRATION STATEMENT

UNDER

THE INVESTMENT COMPANY ACT OF 1940

Amendment No. 69

COLUMBIA ACORN TRUST

227 West Monroe Street, Suite 3000

Chicago, Illinois 60606

Telephone number: 312.634.9200

Charles P. McQuaid Columbia Acorn Trust 227 West Monroe Street, Suite 3000 Chicago, Illinois 60606	Scott R. Plummer c/o Columbia Management Investment Advisers, LLC 225 Franklin Street Boston, MA 02110	Mary C. Moynihan Perkins Coie LLP 700 13th Street, N.W., Suite 600 Washington, D.C. 20005
(Agents for service)

It is proposed that this filing will become effective:

x immediately upon filing pursuant to rule 485(b)

¨ on                      pursuant to rule 485(b)

¨ 60 days after filing pursuant to rule 485(a)(1)

¨ on                      pursuant to rule 485(a)(l)

¨ 75 days after filing pursuant to rule 485(a)(2)

¨ on                      pursuant to rule 485(a)(2).

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933 and the Investment Company Act of 1940, the Registrant certifies that it meets all the requirements for effectiveness of this post-effective amendment pursuant to Rule 485(b) under the Securities Act of 1933 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Chicago and State of Illinois on May 22, 2012.

COLUMBIA ACORN TRUST
By	/S/    CHARLES P. MCQUAID
	Charles P. McQuaid, President

Pursuant to the requirements of the Securities Act of 1933, this amendment to the registration statement has been signed below by the following persons in the capacities and on the dates indicated.

Name	Title		Date
/S/    LAURA M. BORN	Trustee and Chair	)
Laura M. Born		)
		)
/S/    MICHELLE L. COLLINS	Trustee	)
Michelle L. Collins		)
		)
/S/    MAUREEN M. CULHANE	Trustee	)
Maureen M. Culhane		)
		)
/S/    MARGARET M. EISEN	Trustee	)
Margaret M. Eisen		)
		)
/S/    JOHN C. HEATON	Trustee	)
John C. Heaton		)
		)
/S/    STEVEN N. KAPLAN	Trustee	)
Steven N. Kaplan		)
		)
/S/    DAVID J. RUDIS	Trustee	)	May 22, 2012
David J. Rudis		)
		)
/S/    DAVID B. SMALL	Trustee	)
David B. Small		)
		)
/S/    CHARLES P. MCQUAID	Trustee and President (principal executive	)
Charles P. McQuaid	officer)	)
		)
/S/    BRUCE H. LAUER	Treasurer (principal financial and	)
Bruce H. Lauer	accounting officer)	)

Index of Exhibits Filed with this Amendment

Exhibit Number	Exhibit
EX-101.INS	XBRL Instance Document
EX-101.SCH	XBRL Taxonomy Extension Schema Document
EX-101.CAL	XBRL Taxonomy Extension Calculation Linkbase
EX-101.DEF	XBRL Taxonomy Extension Definition Linkbase
EX-101.LAB	XBRL Taxonomy Extension Labels Linkbase
EX-101.PRE	XBRL Taxonomy Extension Presentation Linkbase

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Annual Fund Operating Expenses	0 Months Ended
	May 01, 2012
(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund) | Class A Shares
Operating Expenses:
Management fees	0.64%
Distribution and/or service (Rule 12b-1) fees	0.25%
Other expenses	0.22%	[1]
Total annual Fund operating expenses	1.11%
(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund) | Class C Shares
Operating Expenses:
Management fees	0.64%
Distribution and/or service (Rule 12b-1) fees	1.00%
Other expenses	0.30%	[1]
Total annual Fund operating expenses	1.94%
(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund) | Class I Shares
Operating Expenses:
Management fees	0.64%
Distribution and/or service (Rule 12b-1) fees	none
Other expenses	0.07%	[1]
Total annual Fund operating expenses	0.71%
(Columbia Acorn Fund B) | (Columbia Acorn Fund) | Class B Shares
Operating Expenses:
Management fees	0.64%
Distribution and/or service (Rule 12b-1) fees	0.75%
Other expenses	0.42%	[1]
Total annual Fund operating expenses	1.81%
(Columbia Acorn Fund Z) | (Columbia Acorn Fund) | Class Z Shares
Operating Expenses:
Management fees	0.64%
Distribution and/or service (Rule 12b-1) fees	none
Other expenses	0.13%	[1]
Total annual Fund operating expenses	0.77%
(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | Class A Shares
Operating Expenses:
Management fees	0.76%
Distribution and/or service (Rule 12b-1) fees	0.25%
Other expenses	0.38%	[1]
Total annual Fund operating expenses	1.39%
Fee waivers and/or reimbursements	(0.04%)	[2]
Total annual Fund operating expenses after fee waivers and/or reimbursements	1.35%
(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | Class C Shares
Operating Expenses:
Management fees	0.76%
Distribution and/or service (Rule 12b-1) fees	1.00%
Other expenses	0.40%	[1]
Total annual Fund operating expenses	2.16%
Fee waivers and/or reimbursements	(0.02%)	[2]
Total annual Fund operating expenses after fee waivers and/or reimbursements	2.14%
(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | Class I Shares
Operating Expenses:
Management fees	0.76%
Distribution and/or service (Rule 12b-1) fees	none
Other expenses	0.10%	[1]
Total annual Fund operating expenses	0.86%
Fee waivers and/or reimbursements	none
Total annual Fund operating expenses after fee waivers and/or reimbursements	0.86%
(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | Class R Shares
Operating Expenses:
Management fees	0.76%
Distribution and/or service (Rule 12b-1) fees	0.50%
Other expenses	0.16%	[1]
Total annual Fund operating expenses	1.42%
Fee waivers and/or reimbursements	none
Total annual Fund operating expenses after fee waivers and/or reimbursements	1.42%
(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | Class R5 Shares
Operating Expenses:
Management fees	0.76%
Distribution and/or service (Rule 12b-1) fees	none
Other expenses	0.11%	[1]
Total annual Fund operating expenses	0.87%
Fee waivers and/or reimbursements	none
Total annual Fund operating expenses after fee waivers and/or reimbursements	0.87%
(Columbia Acorn International B) | (Columbia Acorn International) | Class B Shares
Operating Expenses:
Management fees	0.76%
Distribution and/or service (Rule 12b-1) fees	0.75%
Other expenses	0.60%	[1]
Total annual Fund operating expenses	2.11%
Fee waivers and/or reimbursements	(0.03%)	[3]
Total annual Fund operating expenses after fee waivers and/or reimbursements	2.08%
(Columbia Acorn International Z) | (Columbia Acorn International) | Class Z Shares
Operating Expenses:
Management fees	0.76%
Distribution and/or service (Rule 12b-1) fees	none
Other expenses	0.22%	[1]
Total annual Fund operating expenses	0.98%
(Columbia Acorn USA A,C & I) | (Columbia Acorn USA) | Class A Shares
Operating Expenses:
Management fees	0.86%
Distribution and/or service (Rule 12b-1) fees	0.25%
Other expenses	0.22%	[1]
Total annual Fund operating expenses	1.33%
(Columbia Acorn USA A,C & I) | (Columbia Acorn USA) | Class C Shares
Operating Expenses:
Management fees	0.86%
Distribution and/or service (Rule 12b-1) fees	1.00%
Other expenses	0.32%	[1]
Total annual Fund operating expenses	2.18%
(Columbia Acorn USA A,C & I) | (Columbia Acorn USA) | Class I Shares
Operating Expenses:
Management fees	0.86%
Distribution and/or service (Rule 12b-1) fees	none
Other expenses	0.09%	[1]
Total annual Fund operating expenses	0.95%
(Columbia Acorn USA B) | (Columbia Acorn USA) | Class B Shares
Operating Expenses:
Management fees	0.86%
Distribution and/or service (Rule 12b-1) fees	0.75%
Other expenses	0.49%	[1]
Total annual Fund operating expenses	2.10%
(Columbia Acorn USA Z) | (Columbia Acorn USA) | Class Z Shares
Operating Expenses:
Management fees	0.86%
Distribution and/or service (Rule 12b-1) fees	none
Other expenses	0.19%	[1]
Total annual Fund operating expenses	1.05%
(Columbia Acorn Select A,C & I) | (Columbia Acorn Select) | Class A Shares
Operating Expenses:
Management fees	0.82%
Distribution and/or service (Rule 12b-1) fees	0.25%
Other expenses	0.28%	[1]
Total annual Fund operating expenses	1.35%
(Columbia Acorn Select A,C & I) | (Columbia Acorn Select) | Class C Shares
Operating Expenses:
Management fees	0.82%
Distribution and/or service (Rule 12b-1) fees	1.00%
Other expenses	0.35%	[1]
Total annual Fund operating expenses	2.17%
(Columbia Acorn Select A,C & I) | (Columbia Acorn Select) | Class I Shares
Operating Expenses:
Management fees	0.82%
Distribution and/or service (Rule 12b-1) fees	none
Other expenses	0.09%	[1]
Total annual Fund operating expenses	0.91%
(Columbia Acorn Select B) | (Columbia Acorn Select) | Class B Shares
Operating Expenses:
Management fees	0.82%
Distribution and/or service (Rule 12b-1) fees	0.75%
Other expenses	0.48%	[1]
Total annual Fund operating expenses	2.05%
(Columbia Acorn Select Z) | (Columbia Acorn Select) | Class Z Shares
Operating Expenses:
Management fees	0.82%
Distribution and/or service (Rule 12b-1) fees	none
Other expenses	0.18%	[1]
Total annual Fund operating expenses	1.00%
(Columbia Acorn International Select A,C & I) | (Columbia Acorn International Select) | Class A Shares
Operating Expenses:
Management fees	0.94%
Distribution and/or service (Rule 12b-1) fees	0.25%
Other expenses	0.43%	[1]
Total annual Fund operating expenses	1.62%
(Columbia Acorn International Select A,C & I) | (Columbia Acorn International Select) | Class C Shares
Operating Expenses:
Management fees	0.94%
Distribution and/or service (Rule 12b-1) fees	1.00%
Other expenses	0.50%	[1]
Total annual Fund operating expenses	2.44%
(Columbia Acorn International Select A,C & I) | (Columbia Acorn International Select) | Class I Shares
Operating Expenses:
Management fees	0.94%
Distribution and/or service (Rule 12b-1) fees	none
Other expenses	0.14%	[1]
Total annual Fund operating expenses	1.08%
(Columbia Acorn International Select B) | (Columbia Acorn International Select) | Class B Shares
Operating Expenses:
Management fees	0.94%
Distribution and/or service (Rule 12b-1) fees	0.75%
Other expenses	0.63%	[1]
Total annual Fund operating expenses	2.32%
(Columbia Acorn International Select Z) | (Columbia Acorn International Select) | Class Z Shares
Operating Expenses:
Management fees	0.94%
Distribution and/or service (Rule 12b-1) fees	none
Other expenses	0.31%	[1]
Total annual Fund operating expenses	1.25%
(Columbia Thermostat Fund A&C) | (Columbia Thermostat Fund) | Class A Shares
Operating Expenses:
Management fees	0.10%
Distribution and/or service (Rule 12b-1) fees	0.25%
Other expenses	0.46%	[1]
Acquired Fund Fees and Expenses	0.65%
Total annual Fund operating expenses	1.46%	[4]
Fee waivers and/or reimbursements	(0.31%)	[5]
Total annual Fund operating expenses after fee waivers and/or reimbursements	1.15%
(Columbia Thermostat Fund A&C) | (Columbia Thermostat Fund) | Class C Shares
Operating Expenses:
Management fees	0.10%
Distribution and/or service (Rule 12b-1) fees	1.00%
Other expenses	0.46%	[1]
Acquired Fund Fees and Expenses	0.65%
Total annual Fund operating expenses	2.21%	[4]
Fee waivers and/or reimbursements	(0.31%)	[5]
Total annual Fund operating expenses after fee waivers and/or reimbursements	1.90%
(Columbia Thermostat Fund B) | (Columbia Thermostat Fund) | Class B Shares
Operating Expenses:
Management fees	0.10%
Distribution and/or service (Rule 12b-1) fees	0.75%
Other expenses	0.52%	[1]
Acquired Fund Fees and Expenses	0.65%
Total annual Fund operating expenses	2.02%	[4]
Fee waivers and/or reimbursements	(0.37%)	[5]
Total annual Fund operating expenses after fee waivers and/or reimbursements	1.65%
(Columbia Thermostat Fund Z) | (Columbia Thermostat Fund) | Class Z Shares
Operating Expenses:
Management fees	0.10%
Distribution and/or service (Rule 12b-1) fees	none
Other expenses	0.28%	[1]
Acquired Fund Fees and Expenses	0.65%
Total annual Fund operating expenses	1.03%	[4]
Fee waivers and/or reimbursements	(0.13%)	[5]
Total annual Fund operating expenses after fee waivers and/or reimbursements	0.90%
(Columbia Acorn European Fund A,C & I) | (Columbia Acorn European Fund) | Class A Shares
Operating Expenses:
Management fees	1.19%
Distribution and/or service (Rule 12b-1) fees	0.25%
Other expenses	18.29%	[1]
Total annual Fund operating expenses	19.73%
Fee waivers and/or reimbursements	(17.98%)	[6]
Total annual Fund operating expenses after fee waivers and/or reimbursements	1.75%
(Columbia Acorn European Fund A,C & I) | (Columbia Acorn European Fund) | Class C Shares
Operating Expenses:
Management fees	1.19%
Distribution and/or service (Rule 12b-1) fees	1.00%
Other expenses	19.93%	[1]
Total annual Fund operating expenses	22.12%
Fee waivers and/or reimbursements	(19.62%)	[6]
Total annual Fund operating expenses after fee waivers and/or reimbursements	2.50%
(Columbia Acorn European Fund A,C & I) | (Columbia Acorn European Fund) | Class I Shares
Operating Expenses:
Management fees	1.19%
Distribution and/or service (Rule 12b-1) fees	none
Other expenses	17.78%	[1]
Total annual Fund operating expenses	18.97%
Fee waivers and/or reimbursements	(17.66%)	[6]
Total annual Fund operating expenses after fee waivers and/or reimbursements	1.31%
(Columbia Acorn European Fund Z) | (Columbia Acorn European Fund) | Class Z Shares
Operating Expenses:
Management fees	1.19%
Distribution and/or service (Rule 12b-1) fees	none
Other expenses	17.83%	[1]
Total annual Fund operating expenses	19.02%
Fee waivers and/or reimbursements	(17.52%)	[7]
Total annual Fund operating expenses after fee waivers and/or reimbursements	1.50%
(Columbia Acorn Emerging Markets Fund A,C & I) | (Columbia Acorn Emerging Markets Fund) | Class A Shares
Operating Expenses:
Management fees	1.25%
Distribution and/or service (Rule 12b-1) fees	0.25%
Other expenses	12.72%	[1]
Total annual Fund operating expenses	14.22%	[8]
Fee waivers and/or reimbursements	(12.37%)	[9]
Total annual Fund operating expenses after fee waivers and/or reimbursements	1.85%
(Columbia Acorn Emerging Markets Fund A,C & I) | (Columbia Acorn Emerging Markets Fund) | Class C Shares
Operating Expenses:
Management fees	1.25%
Distribution and/or service (Rule 12b-1) fees	1.00%
Other expenses	13.09%	[1]
Total annual Fund operating expenses	15.34%	[8]
Fee waivers and/or reimbursements	(12.74%)	[9]
Total annual Fund operating expenses after fee waivers and/or reimbursements	2.60%
(Columbia Acorn Emerging Markets Fund A,C & I) | (Columbia Acorn Emerging Markets Fund) | Class I Shares
Operating Expenses:
Management fees	1.25%
Distribution and/or service (Rule 12b-1) fees	none
Other expenses	12.05%	[1]
Total annual Fund operating expenses	13.30%	[8]
Fee waivers and/or reimbursements	(11.89%)	[9]
Total annual Fund operating expenses after fee waivers and/or reimbursements	1.41%
(Columbia Acorn Emerging Markets Fund Z) | (Columbia Acorn Emerging Markets Fund) | Class Z Shares
Operating Expenses:
Management fees	1.25%
Distribution and/or service (Rule 12b-1) fees	none
Other expenses	12.10%	[1]
Total annual Fund operating expenses	13.35%	[8]
Fee waivers and/or reimbursements	(11.75%)	[10]
Total annual Fund operating expenses after fee waivers and/or reimbursements	1.60%

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[2] Columbia Management Investment Services Corp., the Fund's transfer agent, has contractually agreed, through August 14, 2013, to waive a portion of total annual Fund operating expenses attributable to transfer agency fees incurred by Class A shares and Class C shares. Pursuant to this agreement, total annual Fund operating expenses will be reduced by 0.04% for Class A shares and 0.02% for Class C shares.

[3] Columbia Management Investment Services Corp., the Fund's transfer agent, has contractually agreed, through August 14, 2013, to waive a portion of total annual Fund operating expenses attributable to transfer agency fees incurred by Class B shares. Pursuant to this agreement, total annual Fund operating expenses will be reduced by 0.03% for Class B shares.

[4] Total annual Fund operating expenses include the annualized average weighted fees and expenses of acquired funds (underlying Portfolio Funds). As a result, the amount shown is higher than the ratio of expenses to average net assets included in Financial Highlights, which reflects only those expenses paid directly by the Fund.

[5] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that ordinary operating expenses (excluding distribution and service fees, interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies) do not exceed the annual rate of 0.25% of the Fund's average daily net assets, through April 30, 2013. The figure shown here is the amount of expected waivers and/or reimbursements. This fee and expense arrangement may only be modified or amended with approval from all parties to such arrangement, including the Fund and the Investment Manager.

[6] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that the ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) do not exceed the annual rates of 1.75%, 2.50% and 1.31% of the Fund's average daily net assets attributable to Class A, Class C and Class I shares, respectively, through April 30, 2013. The Investment Manager may recoup any fees waived and/or expenses reimbursed with respect to any share class of the Fund for a one-year period following the date of such fee waiver and/or reimbursement if such recovery does not cause the Fund's ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) to exceed the annual rates set forth in this prospectus, or to exceed such annual rate as may be in place at the time of the recoupment, whichever is less. This expense arrangement may only be modified or amended with approval from all parties to such arrangements, including the Fund and the Investment Manager.

[7] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that the ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) do not exceed the annual rate of 1.50% of the Fund's average daily net assets attributable to Class Z shares, through April 30, 2013. The Investment Manager may recoup any fees waived and/or expenses reimbursed with respect to any share class of the Fund for a one-year period following the date of such fee waiver and/or reimbursement if such recovery does not cause the Fund's ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) to exceed the annual rates set forth in this prospectus, or to exceed such annual rate as may be in place at the time of the recoupment, whichever is less. This expense arrangement may only be modified or amended with approval from all parties to such arrangements, including the Fund and the Investment Manager.

[8] During its initial fiscal period, the Fund had acquired fund fees and expenses of 0.04% on an annualized basis. Based on assumptions as to the Fund's expected investments in other investment companies during the current fiscal year, acquired fund fees and expenses are expected to be less than 0.01%.

[9] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that the ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) do not exceed the annual rates of 1.85%, 2.60% and 1.41% of the Fund's average daily net assets attributable to Class A, Class C and Class I shares, respectively, through April 30, 2013. The Investment Manager may recoup any fees waived and/or expenses reimbursed with respect to any share class of the Fund for a one-year period following the date of such fee waiver and/or reimbursement if such recovery does not cause the Fund's ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) to exceed the annual rates set forth in this prospectus, or to exceed such annual rate as may be in place at the time of the recoupment, whichever is less. This expense arrangement may only be modified or amended with approval from all parties to such arrangements, including the Fund and the Investment Manager.

[10] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that the ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) do not exceed the annual rate of 1.60% of the Fund's average daily net assets attributable to Class Z shares, through April 30, 2013. The Investment Manager may recoup any fees waived and/or expenses reimbursed with respect to any share class of the Fund for a one-year period following the date of such fee waiver and/or reimbursement if such recovery does not cause the Fund's ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) to exceed the annual rates set forth in this prospectus, or to exceed such annual rate as may be in place at the time of the recoupment, whichever is less. This expense arrangement may only be modified or amended with approval from all parties to such arrangements, including the Fund and the Investment Manager.

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(Columbia Acorn USA B) | (Columbia Acorn USA)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn USA)		Class B Shares (Columbia Acorn USA B)
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	[1]	5.00%

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn USA)		Class B Shares (Columbia Acorn USA B)
Management fees		0.86%
Distribution and/or service (Rule 12b-1) fees		0.75%
Other expenses	[1]	0.49%
Total annual Fund operating expenses		2.10%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class B shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn USA) (USD $)	1 Year	3 Years	5 Years	10 Years
Class B Shares (Columbia Acorn USA B)	713	958	1,329	2,234

Expense Example, No Redemption (Columbia Acorn USA) (USD $)	1 Year	3 Years	5 Years	10 Years
Class B Shares (Columbia Acorn USA B)	213	658	1,129	2,234

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 20% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 80% of its net assets (plus any borrowings for investment purposes) in U.S. companies.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class B shares has varied from year to year.

Year by Year Total Return (%) as of December 31 Each Year

^[1]

Best and Worst Quarterly Returns During this Period

Best:    3rd quarter 2009:    23.15%

Worst:   4th quarter 2008:   -28.08%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns for each period with those of the Russell 2000 Index. This index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index.

Average Annual Total Returns (Columbia Acorn USA) (Columbia Acorn USA B)	1 Year	5 Years	10 Years
Class B Shares	(10.36%)	(0.45%)	5.25%
Class B Shares returns after taxes on distributions	(10.46%)	(0.77%)	4.95%
Class B Shares returns after taxes on distributions and sale of Fund shares	(6.60%)	(0.37%)	4.59%
Russell 2000 Index (reflects no deductions for fees, expenses or taxes)	(4.18%)	0.15%	5.62%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

[1] This charge decreases over time. See About Class B Shares - Sales Charges and Commissions for details.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] Year-to-date return as of March 31, 2012: 16.06%

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(Columbia Acorn USA A,C & I) | (Columbia Acorn USA)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds. More information about these and other discounts is available from your financial advisor, in the Choosing a Share Class section beginning on page 17 of this prospectus and in Appendix D to the Statement of Additional Information under Sales Charge Waivers beginning on page D-1.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn USA A,C & I) (Columbia Acorn USA)	Class A Shares		Class C Shares		Class I Shares
Maximum sales charge (load) imposed on purchases, as a % of offering price	5.75%
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[1]	1.00%	[2]

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn USA A,C & I) (Columbia Acorn USA)		Class A Shares	Class C Shares	Class I Shares
Management fees		0.86%	0.86%	0.86%
Distribution and/or service (Rule 12b-1) fees		0.25%	1.00%	none
Other expenses	[1]	0.22%	0.32%	0.09%
Total annual Fund operating expenses		1.33%	2.18%	0.95%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class A, Class C or Class I shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn USA) (Columbia Acorn USA A,C & I) (USD $)	1 Year	3 Years	5 Years	10 Years
Class A Shares	703	972	1,262	2,084
Class C Shares	321	682	1,169	2,513
Class I Shares	97	303	525	1,166

Expense Example, No Redemption (Columbia Acorn USA) (USD $)	1 Year	3 Years	5 Years	10 Years
Class C Shares (Columbia Acorn USA A,C & I)	221	682	1,169	2,513

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 20% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 80% of its net assets (plus any borrowings for investment purposes) in U.S. companies.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The inception date for the Fund's Class I shares is September 27, 2010. The returns shown for Class I shares include the returns of the Fund's Class Z shares for periods prior to the inception date of Class I shares. Except for differences in expenses, Class I shares have annual returns substantially similar to those of Class Z shares, which are not offered in this prospectus, because all classes of the Fund's shares invest in the same portfolio of securities.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class A shares has varied from year to year. These returns do not reflect deductions of sales charges, if any, paid by investors and would be lower if they did.

Year by Year Total Return (%) as of December 31 Each Year

^[1]

Best and Worst Quarterly Returns During this Period

Best:    3rd quarter 2009:    23.37%

Worst:   4th quarter 2008:   -27.99%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns for each period with those of the Russell 2000 Index. This index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index.

Average Annual Total Returns (Columbia Acorn USA) (Columbia Acorn USA A,C & I)	1 Year	5 Years	10 Years
Class A Shares	(10.66%)	(0.65%)	5.30%
Class A Shares returns after taxes on distributions	(10.74%)	(0.95%)	5.02%
Class A Shares returns after taxes on distributions and sale of Fund shares	(6.81%)	(0.55%)	4.63%
Class C Shares	(6.86%)	(0.25%)	5.14%
Class I Shares	(4.88%)	0.83%	6.31%
Russell 2000 Index (reflects no deductions for fees, expenses or taxes)	(4.18%)	0.15%	5.62%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown only for Class A shares and will vary for other share classes.

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

[1] Contingent deferred sales charges (CDSC) on certain investments of between $1 million and $50 million redeemed within 18 months of purchase, charged as follows: 1.00% CDSC if redeemed within 12 months of purchase, and 0.50% CDSC if redeemed more than 12, but less than 18, months of purchase, with certain limited exceptions.

[2] This charge applies to investors who buy Class C shares and redeem them within one year of purchase, with certain limited exceptions.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] Year-to-date return as of March 31, 2012: 16.27%

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(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds. More information about these and other discounts is available from your financial advisor, in the Choosing a Share Class section beginning on page 17 of this prospectus and in Appendix D to the Statement of Additional Information under Sales Charge Waivers beginning on page D-1.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn Fund A,C & I) (Columbia Acorn Fund)	Class A Shares		Class C Shares		Class I Shares
Maximum sales charge (load) imposed on purchases, as a % of offering price	5.75%
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[1]	1.00%	[2]

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn Fund A,C & I) (Columbia Acorn Fund)		Class A Shares	Class C Shares	Class I Shares
Management fees		0.64%	0.64%	0.64%
Distribution and/or service (Rule 12b-1) fees		0.25%	1.00%	none
Other expenses	[1]	0.22%	0.30%	0.07%
Total annual Fund operating expenses		1.11%	1.94%	0.71%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class A, Class C or Class I shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn Fund) (Columbia Acorn Fund A,C & I) (USD $)	1 Year	3 Years	5 Years	10 Years
Class A Shares	682	908	1,151	1,849
Class C Shares	297	609	1,047	2,264
Class I Shares	73	227	395	883

Expense Example, No Redemption (Columbia Acorn Fund) (USD $)	1 Year	3 Years	5 Years	10 Years
Class C Shares (Columbia Acorn Fund A,C & I)	197	609	1,047	2,264

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 18% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion. Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Brazil).

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment. Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The inception date for the Fund's Class I shares is September 27, 2010. The returns shown for Class I shares include the returns of the Fund's Class Z shares for periods prior to the inception date of Class I shares. Except for differences in expenses, Class I shares have annual returns substantially similar to those of Class Z shares, which are not offered in this prospectus, because all classes of the Fund's shares invest in the same portfolio of securities.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class A shares has varied from year to year. These returns do not reflect deductions of sales charges, if any, paid by investors and would be lower if they did.

Year by Year Total Return (%) as of December 31 Each Year

^[1]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    20.87%

Worst:   4th quarter 2008:   -25.19%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns for each period with those of the Russell 2500 Index, the Fund's primary benchmark, the Standard & Poor's (S&P) 500® Index and the Russell 2000 Index. The Russell 2500 Index measures the performance of the 2,500 smallest companies in the Russell 3000 Index, which represents approximately 17% of the total market capitalization of the Russell 3000 Index. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in small and mid-sized companies, the comparison to the S&P 500® Index is presented to show performance against a widely recognized market index. The Russell 2000 Index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index. The Russell 2000 Index shows how the Fund's performance compares to a widely recognized broad based index of companies with somewhat lower capitalization than the Fund's primary benchmark.

Average Annual Total Returns (Columbia Acorn Fund) (Columbia Acorn Fund A,C & I)	1 Year	5 Years	10 Years
Class A Shares	(10.36%)	0.62%	7.21%
Class A Shares returns after taxes on distributions	(10.94%)	0.10%	6.65%
Class A Shares returns after taxes on distributions and sale of Fund shares	(5.94%)	0.53%	6.32%
Class C Shares	(6.53%)	1.02%	7.04%
Class I Shares	(4.57%)	2.14%	8.25%
Russell 2500 Index (reflects no deductions for fees, expenses or taxes)	(2.51%)	1.24%	6.57%
S&P 500® Index (reflects no deductions for fees, expenses or taxes)	2.11%	(0.25%)	2.92%
Russell 2000 Index (reflects no deductions for fees, expenses or taxes)	(4.18%)	0.15%	5.62%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown only for Class A shares and will vary for other share classes.

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

[1] Contingent deferred sales charges (CDSC) on certain investments of between $1 million and $50 million redeemed within 18 months of purchase, charged as follows: 1.00% CDSC if redeemed within 12 months of purchase, and 0.50% CDSC if redeemed more than 12, but less than 18, months of purchase, with certain limited exceptions.

[2] This charge applies to investors who buy Class C shares and redeem them within one year of purchase, with certain limited exceptions.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] Year-to-date return as of March 31, 2012: 15.43%

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(Columbia Acorn International B) | (Columbia Acorn International)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn International)		Class B Shares (Columbia Acorn International B)
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	[1]	5.00%

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn International)		Class B Shares (Columbia Acorn International B)
Management fees		0.76%
Distribution and/or service (Rule 12b-1) fees		0.75%
Other expenses	[1]	0.60%
Total annual Fund operating expenses		2.11%
Fee waivers and/or reimbursements	[2]	(0.03%)
Total annual Fund operating expenses after fee waivers and/or reimbursements		2.08%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class B shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn International) (USD $)	1 Year	3 Years	5 Years	10 Years
Class B Shares (Columbia Acorn International B)	711	958	1,331	2,255

Expense Example, No Redemption (Columbia Acorn International) (USD $)	1 Year	3 Years	5 Years	10 Years
Class B Shares (Columbia Acorn International B)	211	658	1,131	2,255

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 32% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 75% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Brazil).

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class B shares has varied from year to year.

Year by Year Total Return (%) as of December 31 Each Year

^[1]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    32.92%

Worst:   3rd quarter 2008:   -23.87%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns, for each period, with those of the Standard & Poor's (S&P) Global Ex-U.S. Between $500 Million and $5 Billion® Index, the Fund's primary benchmark, the S&P Global Ex-U.S. SmallCap® Index and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Global Ex-U.S. Between $500 Million and $5 Billion® Index is a subset of the broad market selected by the index sponsor that represents the mid- and small-cap developed and emerging markets, excluding the United States. The S&P Global Ex-U.S. SmallCap® Index is an unmanaged index consisting of the bottom 20% of institutionally investable capital of developed and emerging countries, excluding the United States. The performance of the S&P Global Ex-U.S. Small Cap® Index is provided to show how the Fund's performance compares to foreign market performance with a similar geographic distribution and wider market cap range than the Fund's primary benchmark. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund's performance compares to a widely recognized broad based index of foreign market performance.

Average Annual Total Returns (Columbia Acorn International) (Columbia Acorn International B)	1 Year	5 Years	10 Years
Class B Shares	(19.07%)	(1.13%)	9.12%
Class B Shares returns after taxes on distributions	(19.63%)	(1.53%)	8.74%
Class B Shares returns after taxes on distributions and sale of Fund shares	(12.13%)	(0.90%)	8.20%
S&P Global Ex-U.S. Between $500 Million and $5 Billion® Index (reflects no deductions for fees, expenses or taxes)	(16.94%)	(0.58%)	11.10%
S&P Global Ex-U.S. SmallCap® Index (reflects no deductions for fees, expenses or taxes)	(17.40%)	(2.14%)	10.33%
MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)	(12.14%)	(4.72%)	4.67%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

[1] This charge decreases over time. See About Class B Shares - Sales Charges and Commissions for details.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[2] Columbia Management Investment Services Corp., the Fund's transfer agent, has contractually agreed, through August 14, 2013, to waive a portion of total annual Fund operating expenses attributable to transfer agency fees incurred by Class B shares. Pursuant to this agreement, total annual Fund operating expenses will be reduced by 0.03% for Class B shares.

[1] Year-to-date return as of March 31, 2012: 14.77%

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(Columbia Acorn Emerging Markets Fund A,C & I) | (Columbia Acorn Emerging Markets Fund)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds. More information about these and other discounts is available from your financial advisor, in the Choosing a Share Class section beginning on page 18 of this prospectus and in Appendix D to the Statement of Additional Information under Sales Charge Waivers beginning on page D-1.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn Emerging Markets Fund A,C & I) (Columbia Acorn Emerging Markets Fund)	Class A Shares		Class C Shares		Class I Shares
Maximum sales charge (load) imposed on purchases, as a % of offering price	5.75%
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[1]	1.00%	[2]

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn Emerging Markets Fund A,C & I) (Columbia Acorn Emerging Markets Fund)		Class A Shares	Class C Shares	Class I Shares
Management fees		1.25%	1.25%	1.25%
Distribution and/or service (Rule 12b-1) fees		0.25%	1.00%	none
Other expenses	[1]	12.72%	13.09%	12.05%
Total annual Fund operating expenses	[2]	14.22%	15.34%	13.30%
Fee waivers and/or reimbursements	[3]	(12.37%)	(12.74%)	(11.89%)
Total annual Fund operating expenses after fee waivers and/or reimbursements		1.85%	2.60%	1.41%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class A, Class C or Class I shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire on April 30, 2013, they are only reflected in the 1 year example and the first year of the 3 year example.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn Emerging Markets Fund) (Columbia Acorn Emerging Markets Fund A,C & I) (USD $)	1 Year	3 Years
Class A Shares	752	3,268
Class C Shares	363	3,088
Class I Shares	144	2,675

Expense Example, No Redemption (Columbia Acorn Emerging Markets Fund) (USD $)	1 Year	3 Years
Class C Shares (Columbia Acorn Emerging Markets Fund A,C & I)	263	3,088

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 9% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 80% of its net assets (plus any borrowing for investment purposes) in companies located in emerging market countries, including frontier market countries. Emerging market countries are those countries whose economies are developing or emerging from underdevelopment (for example, China, India, Poland and Turkey). Frontier market countries generally have smaller economies and even less developed capital markets than traditional emerging market countries (for example, Vietnam, Colombia, Nigeria and Kazakhstan). For purposes of the Fund's policies, the Fund may invest in a company if (i) it is domiciled in, or the principal trading market for its securities is in, an emerging market country, (ii) it derives 50% or more of its economic value from goods produced, sales made or services performed or has at least 50% of its assets in an emerging market country or countries or (iii) it is a holding company that predominantly holds shares in such companies. The Fund may invest in a variety of countries, industries and sectors and does not attempt to invest a specific percentage of its assets in any given country, industry or sector.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion. Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to initially invest in a limited number of companies (generally under 100), offering the potential to provide above-average growth over time.

Generally, the Investment Manager will determine which countries are emerging market countries by reference to the countries included in the S&P Emerging Markets Broad Market Index (BMI), and will determine which countries are frontier market countries by reference to the countries included in the S&P Frontier BMI. In addition, the Fund may invest in certain developing market countries that are not included in either the S&P Emerging Markets BMI or the S&P Frontier BMI (for example, Serbia and Senegal), but which are included on another independent third-party listing of emerging market and/or frontier market countries. The Investment Manager will make all determinations as to whether a company is an emerging market company at the time of investment. The countries that comprise emerging market countries, including frontier market countries, may change from time to time.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Frontier Market Risk — Frontier market countries generally have smaller economies and even less developed capital markets than traditional emerging market countries and, as a result, the risks of investing in emerging market countries are magnified in frontier market countries. The magnification of risks are the result of: potential for extreme price volatility and illiquidity in frontier market countries; government ownership or control of parts of private sector and of certain companies; trade barriers, exchange controls, managed adjustments in relative currency values and other protectionist measures imposed or negotiated by the countries with which frontier market countries trade; and the relatively new and unsettled securities laws in many frontier market countries.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Currency Risk – Securities denominated in non-U.S. dollar currencies are subject to the risk that, for example, if the value of a foreign currency were to decline against the U.S. dollar, such decline would reduce the U.S. dollar value of any securities held by the Fund denominated in that currency.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Special Situations Risk – Securities of companies that are involved in an initial public offering or a major corporate event, such as a business consolidation or restructuring, which may present special risk because of the high degree of uncertainty that can be associated with such events. Securities issued in initial public offerings often are issued by companies that are in the early stages of development, have a history of little or no revenues and may operate at a loss following the offering. It is possible that there will be no active trading market for the securities after the offering, and that the market price of the securities may be subject to significant and unpredictable fluctuations. Investing in special situations may have a magnified effect on the performance of funds with small amounts of assets.

Performance Information

Because the Fund commenced investment operations on August 19, 2011, no year-by-year total return bar chart or average annual total return table is being presented. The year-by year-total return bar chart and the average annual total return table will be provided after the Fund has annual returns for at least one calendar year.

Recent performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

[1] Contingent deferred sales charges (CDSC) on certain investments of between $1 million and $50 million redeemed within 18 months of purchase, charged as follows: 1.00% CDSC if redeemed within 12 months of purchase, and 0.50% CDSC if redeemed more than 12, but less than 18, months of purchase, with certain limited exceptions.

[2] This charge applies to investors who buy Class C shares and redeem them within one year of purchase, with certain limited exceptions.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[2] During its initial fiscal period, the Fund had acquired fund fees and expenses of 0.04% on an annualized basis. Based on assumptions as to the Fund's expected investments in other investment companies during the current fiscal year, acquired fund fees and expenses are expected to be less than 0.01%.

[3] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that the ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) do not exceed the annual rates of 1.85%, 2.60% and 1.41% of the Fund's average daily net assets attributable to Class A, Class C and Class I shares, respectively, through April 30, 2013. The Investment Manager may recoup any fees waived and/or expenses reimbursed with respect to any share class of the Fund for a one-year period following the date of such fee waiver and/or reimbursement if such recovery does not cause the Fund's ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) to exceed the annual rates set forth in this prospectus, or to exceed such annual rate as may be in place at the time of the recoupment, whichever is less. This expense arrangement may only be modified or amended with approval from all parties to such arrangements, including the Fund and the Investment Manager.

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Shareholder Fees	0 Months Ended
	May 01, 2012
(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund) | Class A Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price	5.75%
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[1]
(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund) | Class C Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[2]
(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund) | Class I Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value
(Columbia Acorn Fund B) | (Columbia Acorn Fund) | Class B Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	5.00%	[3]
(Columbia Acorn Fund Z) | (Columbia Acorn Fund) | Class Z Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price	none
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	none
(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | Class A Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price	5.75%
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[1]
(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | Class C Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[2]
(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | Class I Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value
(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | Class R Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value
(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | Class R5 Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value
(Columbia Acorn International B) | (Columbia Acorn International) | Class B Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	5.00%	[3]
(Columbia Acorn International Z) | (Columbia Acorn International) | Class Z Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price	none
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	none
(Columbia Acorn USA A,C & I) | (Columbia Acorn USA) | Class A Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price	5.75%
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[1]
(Columbia Acorn USA A,C & I) | (Columbia Acorn USA) | Class C Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[2]
(Columbia Acorn USA A,C & I) | (Columbia Acorn USA) | Class I Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value
(Columbia Acorn USA B) | (Columbia Acorn USA) | Class B Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	5.00%	[3]
(Columbia Acorn USA Z) | (Columbia Acorn USA) | Class Z Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price	none
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	none
(Columbia Acorn Select A,C & I) | (Columbia Acorn Select) | Class A Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price	5.75%
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[1]
(Columbia Acorn Select A,C & I) | (Columbia Acorn Select) | Class C Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[2]
(Columbia Acorn Select A,C & I) | (Columbia Acorn Select) | Class I Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value
(Columbia Acorn Select B) | (Columbia Acorn Select) | Class B Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	5.00%	[3]
(Columbia Acorn Select Z) | (Columbia Acorn Select) | Class Z Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price	none
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	none
(Columbia Acorn International Select A,C & I) | (Columbia Acorn International Select) | Class A Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price	5.75%
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[1]
(Columbia Acorn International Select A,C & I) | (Columbia Acorn International Select) | Class C Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[2]
(Columbia Acorn International Select A,C & I) | (Columbia Acorn International Select) | Class I Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value
(Columbia Acorn International Select B) | (Columbia Acorn International Select) | Class B Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	5.00%	[3]
(Columbia Acorn International Select Z) | (Columbia Acorn International Select) | Class Z Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price	none
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	none
(Columbia Thermostat Fund A&C) | (Columbia Thermostat Fund) | Class A Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price	5.75%
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[1]
(Columbia Thermostat Fund A&C) | (Columbia Thermostat Fund) | Class C Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[2]
(Columbia Thermostat Fund B) | (Columbia Thermostat Fund) | Class B Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	5.00%	[3]
(Columbia Thermostat Fund Z) | (Columbia Thermostat Fund) | Class Z Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price	none
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	none
(Columbia Acorn European Fund A,C & I) | (Columbia Acorn European Fund) | Class A Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price	5.75%
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[1]
(Columbia Acorn European Fund A,C & I) | (Columbia Acorn European Fund) | Class C Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[2]
(Columbia Acorn European Fund A,C & I) | (Columbia Acorn European Fund) | Class I Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value
(Columbia Acorn European Fund Z) | (Columbia Acorn European Fund) | Class Z Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price	none
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	none
(Columbia Acorn Emerging Markets Fund A,C & I) | (Columbia Acorn Emerging Markets Fund) | Class A Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price	5.75%
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[1]
(Columbia Acorn Emerging Markets Fund A,C & I) | (Columbia Acorn Emerging Markets Fund) | Class C Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[2]
(Columbia Acorn Emerging Markets Fund A,C & I) | (Columbia Acorn Emerging Markets Fund) | Class I Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value
(Columbia Acorn Emerging Markets Fund Z) | (Columbia Acorn Emerging Markets Fund) | Class Z Shares
Shareholder Fees:
Maximum sales charge (load) imposed on purchases, as a % of offering price	none
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	none

[1] Contingent deferred sales charges (CDSC) on certain investments of between $1 million and $50 million redeemed within 18 months of purchase, charged as follows: 1.00% CDSC if redeemed within 12 months of purchase, and 0.50% CDSC if redeemed more than 12, but less than 18, months of purchase, with certain limited exceptions.

[2] This charge applies to investors who buy Class C shares and redeem them within one year of purchase, with certain limited exceptions.

[3] This charge decreases over time. See About Class B Shares - Sales Charges and Commissions for details.

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(Columbia Acorn International Z) | (Columbia Acorn International)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn International)	Class Z Shares (Columbia Acorn International Z)
Maximum sales charge (load) imposed on purchases, as a % of offering price	none
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn International)		Class Z Shares (Columbia Acorn International Z)
Management fees		0.76%
Distribution and/or service (Rule 12b-1) fees		none
Other expenses	[1]	0.22%
Total annual Fund operating expenses		0.98%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class Z shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn International) (USD $)	1 Year	3 Years	5 Years	10 Years
Class Z Shares (Columbia Acorn International Z)	100	312	542	1,201

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 32% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 75% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Brazil).

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class Z shares has varied from year to year.

Year by Year Total Return (%) as of December 31 Each Year

^[1]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    33.30%

Worst:   3rd quarter 2008:   -23.68%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns, for each period, with those of the Standard & Poor's (S&P) Global Ex-U.S. Between $500 Million and $5 Billion® Index, the Fund's primary benchmark, the S&P Global Ex-U.S. SmallCap® Index and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Global Ex-U.S. Between $500 Million and $5 Billion® Index is a subset of the broad market selected by the index sponsor that represents the mid- and small-cap developed and emerging markets, excluding the United States. The S&P Global Ex-U.S. SmallCap® Index is an unmanaged index consisting of the bottom 20% of institutionally investable capital of developed and emerging countries, excluding the United States. The performance of the S&P Global Ex-U.S. Small Cap® Index is provided to show how the Fund's performance compares to foreign market performance with a similar geographic distribution and wider market cap range than the Fund's primary benchmark. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund's performance compares to a widely recognized broad based index of foreign market performance.

Average Annual Total Returns (Columbia Acorn International) (Columbia Acorn International Z)	1 Year	5 Years	10 Years
Class Z Shares	(14.06%)	0.20%	10.27%
Class Z Shares returns after taxes on distributions	(14.63%)	(0.32%)	9.71%
Class Z Shares returns after taxes on distributions and sale of Fund shares	(8.88%)	0.20%	9.18%
S&P Global Ex-U.S. Between $500 Million and $5 Billion® Index (reflects no deductions for fees, expenses or taxes)	(16.94%)	(0.58%)	11.10%
S&P Global Ex-U.S. SmallCap® Index (reflects no deductions for fees, expenses or taxes)	(17.40%)	(2.14%)	10.33%
MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)	(12.14%)	(4.72%)	4.67%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] Year-to-date return as of March 31, 2012: 15.07%

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(Columbia Acorn Fund B) | (Columbia Acorn Fund)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn Fund)		Class B Shares (Columbia Acorn Fund B)
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	[1]	5.00%

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn Fund)		Class B Shares (Columbia Acorn Fund B)
Management fees		0.64%
Distribution and/or service (Rule 12b-1) fees		0.75%
Other expenses	[1]	0.42%
Total annual Fund operating expenses		1.81%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class B shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn Fund) (USD $)	1 Year	3 Years	5 Years	10 Years
Class B Shares (Columbia Acorn Fund B)	684	869	1,180	1,943

Expense Example, No Redemption (Columbia Acorn Fund) (USD $)	1 Year	3 Years	5 Years	10 Years
Class B Shares (Columbia Acorn Fund B)	184	569	980	1,943

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 18% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion. Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Brazil).

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class B shares has varied from year to year.

Year by Year Total Return (%) as of December 31 Each Year

^[1]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    20.64%

Worst:   4th quarter 2008:   -25.33%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns for each period with those of the Russell 2500 Index, the Fund's primary benchmark, the Standard & Poor's (S&P) 500® Index and the Russell 2000 Index. The Russell 2500 Index measures the performance of the 2,500 smallest companies in the Russell 3000 Index, which represents approximately 17% of the total market capitalization of the Russell 3000 Index. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in small and mid-sized companies, the comparison to the S&P 500® Index is presented to show performance against a widely recognized market index. The Russell 2000 Index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index. The Russell 2000 Index shows how the Fund's performance compares to a widely recognized broad based index of companies with somewhat lower capitalization than the Fund's primary benchmark.

Average Annual Total Returns (Columbia Acorn Fund) (Columbia Acorn Fund B)	1 Year	5 Years	10 Years
Class B Shares	(9.86%)	0.89%	7.17%
Class B Shares returns after taxes on distributions	(10.50%)	0.33%	6.59%
Class B Shares returns after taxes on distributions and sale of Fund shares	(5.51%)	0.76%	6.29%
Russell 2500 Index (reflects no deductions for fees, expenses or taxes)	(2.51%)	1.24%	6.57%
S&P 500® Index (reflects no deductions for fees, expenses or taxes)	2.11%	(0.25%)	2.92%
Russell 2000 Index (reflects no deductions for fees, expenses or taxes)	(4.18%)	0.15%	5.62%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

[1] This charge decreases over time. See About Class B Shares - Sales Charges and Commissions for details.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] Year-to-date return as of March 31, 2012: 15.25%

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(Columbia Thermostat Fund A&C) | (Columbia Thermostat Fund)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds. More information about these and other discounts is available from your financial advisor, in the Choosing a Share Class section beginning on page 28 of this prospectus and in Appendix D to the Statement of Additional Information under Sales Charge Waivers beginning on page D-1.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Thermostat Fund A&C) (Columbia Thermostat Fund)	Class A Shares		Class C Shares
Maximum sales charge (load) imposed on purchases, as a % of offering price	5.75%
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[1]	1.00%	[2]

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Thermostat Fund A&C) (Columbia Thermostat Fund)		Class A Shares	Class C Shares
Management fees		0.10%	0.10%
Distribution and/or service (Rule 12b-1) fees		0.25%	1.00%
Other expenses	[1]	0.46%	0.46%
Acquired Fund Fees and Expenses		0.65%	0.65%
Total annual Fund operating expenses	[2]	1.46%	2.21%
Fee waivers and/or reimbursements	[3]	(0.31%)	(0.31%)
Total annual Fund operating expenses after fee waivers and/or reimbursements		1.15%	1.90%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class A or Class C shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire on April 30, 2013, they are only reflected in the 1 year example and the first year of the 3, 5 and 10 year examples.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Thermostat Fund) (Columbia Thermostat Fund A&C) (USD $)	1 Year	3 Years	5 Years	10 Years
Class A Shares	685	981	1,299	2,196
Class C Shares	293	661	1,156	2,520

Expense Example, No Redemption (Columbia Thermostat Fund) (USD $)	1 Year	3 Years	5 Years	10 Years
Class C Shares (Columbia Thermostat Fund A&C)	193	661	1,156	2,520

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund will indirectly bear the expenses associated with portfolio turnover of the underlying Portfolio Funds in which the Fund invests. Each Portfolio Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A Portfolio Fund's higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when its shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 130% of the average value of its portfolio.

Principal Investment Strategies

The Fund pursues its investment objective by investing in other mutual funds. As a "fund of funds," under normal circumstances, the Fund allocates at least 95% of its net assets (stock/bond assets) among a selected group of stock and bond mutual funds (Portfolio Funds) according to the current level of Standard & Poor's (S&P) 500® Index. Generally, when the S&P 500® Index goes up in relation to predetermined ranges set by Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), the Fund sells a portion of its stock funds and invests more in the bond funds and when the S&P 500® Index goes down in relation to the ranges, the Fund increases its investment in the stock funds. Under normal circumstances, the Fund may invest up to 5% of net assets plus any cash received that day in cash, high quality short-term paper and government securities.

Many asset allocation funds typically move assets from stocks to bonds when the market goes up, and from bonds to stocks when the market goes down. Most asset allocation funds are run by sophisticated investment professionals, who make subjective decisions based on economic and financial data and complex graphs of market behavior. By contrast, the day-to-day investment decisions for the Fund are made according to a single predetermined rule. The temperature in your house is run by a single rule: your thermostat turns on the furnace if your house is too cold or turns on the air conditioner if your house is too warm. This Fund works the same way, so it is named Columbia Thermostat Fund.

Because the Fund invests according to a pre-set program, there is no need for subjective day-to-day management. Although another successful asset allocation strategy might do better than the Fund, the Fund is designed for those who doubt the wisdom of trying to "time" the market and are unsure of the long-term trend of the stock market. The Fund takes psychology out of investing; it avoids the temptation to buy more stocks because the stock market is currently going up or to sell stocks because the market is declining. The Fund operates continuously and substantially automatically, subject to periodic review of the pre-set program by the Investment Manager and the Fund's Board of Trustees. As described more fully below, the Investment Manager has the authority to review the structure and allocation ranges of the stock/bond allocation table and to make any changes considered appropriate.

The Investment Manager chooses the Portfolio Funds to provide participation in the major sectors of the stock and bond markets. If you believe that the stock market will tend to go up most of the time, then you should probably own a fully invested stock fund and use a buy-and-hold strategy. Buy-and-hold was an excellent strategy in the 1982-1999 bull market. However, there have been long periods in the past when buy-and-hold was not the best strategy, such as 1930-1954 and 1969-1981, when the market fluctuated but did not make significant new highs. The Fund may be a good investment choice for you if you believe that the market may fluctuate in a trading range for many years, that a remarkable bull market ended early in 2000 and that the market may not reach significant new highs for many years.

The Fund invests its stock/bond assets among the Portfolio Funds according to an asset allocation table. The current allocation table is set forth below.

Stock/Bond Allocation Table

                                      How the Fund will Invest the Stock/Bond Assets

                                      ----------------------------------------------



Level of the S and P 500(R) Index   	    Stock Percentage     Bond Percentage

---------------------------------           ----------------     ---------------

over 1750                                          10%                90%

over 1700 -- 1750                                  15%                85%

over 1650 -- 1700                                  20%                80%

over 1600 -- 1650                                  25%                75%

over 1550 -- 1600                                  30%                70%

over 1500 -- 1550                                  35%                65%

over 1450 -- 1500                                  40%                60%

over 1400 -- 1450                                  45%                55%

over 1350 -- 1400                                  50%                50%

over 1300 -- 1350                                  55%                45%

over 1250 -- 1300                                  60%                40%

over 1200 -- 1250                                  65%                35%

over 1150 -- 1200                                  70%                30%

over 1100 -- 1150                                  75%                25%

over 1050 -- 1100                                  80%                20%

over 1000 -- 1050                                  85%                15%

1000 and under                                     90%                10%

When the S&P 500® Index moves into a new band on the table, the Fund promptly will rebalance the stock/bond mix to reflect the new S&P 500® Index price level by redeeming shares of some Portfolio Funds and purchasing shares of other Portfolio Funds. The only exception will be a "31-day Rule"; in order to reduce taxable events, after the Fund has increased its percentage allocation to either stock funds or bond funds, it will not decrease that allocation for at least 31 days. Following a change in the Fund's stock/bond mix, if the S&P 500® Index remains within the same band for a while, normal market fluctuations will change the values of the Fund's holdings of stock Portfolio Funds and bond Portfolio Funds. The Investment Manager will invest cash flows from sales (or redemptions) of Fund shares to bring the stock/bond mix back toward the allocation percentages for that S&P 500® Index band. For example, if the S&P 500® Index is in the 1150-1200 band, and the value of the holdings of the stock Portfolio Funds has dropped to 68% of the value of the holdings of all Portfolio Funds, the Investment Manager would invest new cash in the stock Portfolio Funds (or cash for redemptions would come from the bond Portfolio Funds). If the 31-day Rule is in effect, the Investment Manager will invest new cash at the stock/bond percentage allocation as of the latest rebalancing.

As an illustrative example, suppose the following:

 		              Level of the 		           How the Fund will invest

Date		          S and P 500(R) Index                       the Stock/Bond Assets

--------        ---------------------------------------         --------------------------------

Nov. 1             We begin when the market is 1380                  50% stocks, 50% bonds

Dec. 1             The S and P 500(R) goes to 1401              rebalance 45% stocks, 55% bonds

Dec. 6           The S and P 500(R) drops back to 1390              no reversal for 31 days

Jan. 2              The S and P 500(R) is at 1352               rebalance 50% stocks, 50% bonds

Jan. 20            The S and P 500(R) drops to 1349             rebalance 55% stocks, 45% bonds



      The market has made a continuation move by going through a second action level,

          not a reversal move, so the 31-day Rule does not apply in this case.



Jan. 30            The S and P 500(R) goes up to 1355               no reversal for 31 days

Feb. 20              The S and P 500(R) is at 1360              rebalance 50% stocks, 50% bonds

The following table shows the seven stock Portfolio Funds and three bond Portfolio Funds that the Fund currently uses in its "fund of funds" structure and the current allocation percentage for each Portfolio Fund within the stock or bond category. As described more fully below, the Investment Manager may substitute or add additional Portfolio Funds at any time, including funds introduced after the date of this prospectus. The allocation percentage within each stock/bond category is achieved by rebalancing the investments within the category whenever the S&P 500® Index moves into a new band on the allocation table, subject to the 31-day Rule described above. The Fund does not liquidate its investment in one Portfolio Fund in order to invest in another Portfolio Fund except in connection with a rebalancing due to a move of the S&P 500® Index into a new band (or due to a change by the Investment Manager in the stock/bond allocation table to the Portfolio Funds or to the relative allocation among them). Until a subsequent rebalancing, the Fund's investments in, and redemptions from, the stock Portfolio Funds or the bond Portfolio Funds are allocated among the Portfolio Funds in a manner that will reduce any deviation of the relative values of the Fund's holdings of the Funds from the allocation percentages shown below.

Allocation of Stock/Bond Assets Within Asset Classes

Stock Funds                                   Type of Fund 	             Allocation

-------------------------------------  ------------------------------------  -----------

Columbia Acorn Fund                    Small/Mid-cap growth                          15%

Columbia Acorn Select                  Mid-cap growth                                10%

Columbia Acorn International           Small/Mid-cap international growth            20%

Columbia Dividend Income Fund          Large-cap value                               20%

Columbia Large Cap Enhanced Core Fund  Large-cap blend                               10%

Columbia Contrarian Core Fund          Large-cap blend                               15%

Columbia Select Large Cap Growth Fund  Large-cap growth                              10%

Total                                                                               100%



Bond Funds                                    Type of Fund 	             Allocation

-------------------------------------  ------------------------------------  -----------

Columbia Intermediate Bond Fund        Intermediate-term bonds                       50%

Columbia Income Opportunities Fund     High-yield bonds                              30%

Columbia U.S. Treasury Index Fund      U.S. Treasury notes/bonds                     20%

Total                                                                               100%

The Investment Manager has the authority to review the Portfolio Funds and the relative stock/bond allocation percentages among them and to make any changes considered appropriate.

Each of the Portfolio Funds is currently managed by the Investment Manager or its affiliates. The Fund does not pay any sales load on its purchases of shares of the Portfolio Funds. On an annual basis, or on an "emergency" basis if necessary, the Investment Manager reviews the structure, allocation percentages and Portfolio Funds and makes any changes considered appropriate. The Investment Manager typically addresses the following questions:

• Should the stock/bond allocation table be revised (perhaps because the stock market has made a long-term move outside of the bands set forth above)?
• Should there be a change in the Portfolio Funds or should there be a change in the percentage allocations among the stock/bond funds (perhaps because of a change of portfolio managers, change of investment style, change in relative valuation or a reorganization of a Portfolio Fund)?

Any such changes by the Investment Manager are expected to be infrequent.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Allocation Risk – The Fund uses an asset allocation strategy in pursuit of its investment objective. There is a risk that the Fund's allocation among asset classes or investments will cause the Fund's shares to lose value or cause the Fund to underperform other funds with similar investment objectives, or that the investments themselves will not produce the returns expected.

• Investing in Other Funds Risk – The performance of the underlying fund(s) in which the Fund invests could be adversely affected if other entities that invest in the same underlying fund(s) make relatively large investments or redemptions in the underlying fund(s). In addition, because the expenses and costs of the underlying fund(s) are shared by investors in the underlying fund, redemptions by other investors in the underlying fund could result in decreased economies of scale and increased operating expenses for the underlying fund. The Fund, and its shareholders, indirectly bear a portion of the expenses of the underlying fund(s). These transactions might also result in higher brokerage, tax or other costs for the Fund. This risk may be particularly important when one investor owns a substantial portion of any underlying fund. In addition, the Investment Manager has the authority to change the underlying fund(s) in which the Fund invests or to change the percentage of the Fund's investments allocated to each underlying fund. If an underlying fund pays fees to the Investment Manager or its affiliates, such as advisory fees, this could result in the Investment Manager having a potential conflict of interest in selecting the underlying fund(s) in which the Fund invests or in determining the percentage of the Fund's investments allocated to each underlying fund. In addition, the underlying funds are themselves subject to Investment Strategy Risk.

The Fund is subject indirectly to the following risks of the Portfolio Funds:

• Market Risk – Market risk refers to the possibility that the market values of securities that a Portfolio Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Portfolio Fund. Accordingly, an investment in a Portfolio Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Portfolio Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Interest Rate Risk – Debt securities are subject to interest rate risk. In general, if prevailing interest rates rise, the values of debt securities will tend to fall, and if interest rates fall, the values of debt securities will tend to rise. Changes in the value of a debt security usually will not affect the amount of income a Portfolio Fund receives from it but may affect the value of the Portfolio Fund's shares. Interest rate risk is generally greater for debt securities with longer maturities/durations.

• Credit Risk – Credit risk applies to most debt securities, but is generally less of a factor for obligations backed by the "full faith and credit" of the U.S. Government. A Portfolio Fund could lose money if the issuer of a debt security owned by the Fund is unable or perceived to be unable to pay interest or repay principal when it becomes due. Various factors could affect the issuer's actual or perceived willingness or ability to make timely interest or principal payments, including changes in the issuer's financial condition or in general economic conditions. Debt securities backed by an issuer's taxing authority may be subject to legal limits on the issuer's power to increase taxes or otherwise to raise revenue, or may be dependent on legislative appropriation or government aid. Certain debt securities are backed only by revenues derived from a particular project or source, rather than by an issuer's taxing authority, and thus may have a greater risk of default.

• Low and Below Investment Grade Securities Risk – Debt securities with the lowest investment grade rating (e.g., BBB by Standard & Poor's, a division of the McGraw-Hill Companies, Inc. (S&P), or Fitch, Inc. (Fitch) or Baa by Moody's Investors Service, Inc. (Moody's)), or that are below investment grade (which are commonly referred to as "junk bonds") (e.g., BB or below by S&P or Fitch or Ba by Moody's) and unrated securities of comparable quality are more speculative than securities with higher ratings and may experience greater price fluctuations. These securities tend to be more sensitive to credit risk than higher-rated securities, particularly during a downturn in the economy, which is more likely to weaken the ability of the issuers to make principal and interest payments on these securities. These securities typically pay a premium – a higher interest rate or yield – because of the increased risk of loss, including default. These securities also are generally less liquid than higher-rated securities. The securities ratings provided by Moody's, S&P and Fitch are based on analyses by these ratings agencies of the credit quality of the securities and may not take into account every risk related to whether interest or principal will be timely repaid.

• Value Securities Risk – Value securities are securities of companies that may have experienced, for example, adverse business, industry or other developments or may be subject to special risks that have caused the securities to be out of favor and, in turn, potentially undervalued. The market value of a portfolio security may not meet the Investment Manager's future value assessment of that security, or may decline. There is also a risk that it may take longer than expected for the value of these investments to rise to the believed value. In addition, value securities, at times, may not perform as well as growth securities or the stock market in general, and may be out of favor with investors for varying periods of time.

• Growth Securities Risk – Because growth securities typically trade at a higher multiple of earnings than other types of securities, the market values of growth securities may be more sensitive to changes in current or expected earnings than the market values of other types of securities. In addition, growth securities, at times, may not perform as well as value securities or the stock market in general, and may be out of favor with investors for varying periods of time.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Portfolio Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Portfolio Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Index Risk – U.S. Treasury Index Fund's value will generally decline when the performance of its targeted index declines. Because U.S. Treasury Index Fund is designed to track an index before fees and expenses, U.S. Treasury Index Fund cannot purchase other securities that may help offset declines in its index. In addition, because U.S. Treasury Index Fund may not hold all issues included in its index, may not always be fully invested, and bears advisory, administrative and other expenses and transaction costs in trading securities, U.S. Treasury Index Fund's performance may fail to match the performance of its targeted index, after taking expenses into account. It is not possible to invest directly in an index.

• U.S. Government Obligations Risk – While U.S. Treasury obligations are backed by the "full faith and credit" of the U.S. Government, such securities are nonetheless subject to credit risk (i.e., the risk that the U.S. Government may be, or may be perceived to be, unable or unwilling to honor its financial obligations, such as making payments). Securities issued or guaranteed by federal agencies or authorities and U.S. Government-sponsored instrumentalities or enterprises may or may not be backed by the full faith and credit of the U.S. Government. For example, securities issued by the Federal Home Loan Mortgage Corporation, the Federal National Mortgage Association and the Federal Home Loan Banks are neither insured nor guaranteed by the U.S. Government. These securities may be supported by the ability to borrow from the U.S. Treasury or only by the credit of the issuing agency, authority, instrumentality or enterprise and, as a result, are subject to greater credit risk than securities issued or guaranteed by the U.S. Treasury. Securities guaranteed by the Federal Deposit Insurance Corporation under its Temporary Liquidity Guarantee Program (TLGP) are subject to certain risks, including whether such securities will continue to trade in line with recent experience in relation to treasury and government agency securities in terms of yield spread and the volatility of such spread, as well as uncertainty as to how such securities will trade in the secondary market and whether that market will be liquid or illiquid. The TLGP is subject to change. See ABOUT THE FUNDS' INVESTMENTS - U.S. Government and Related Obligations in the Statement of Additional Information for more information.

• Derivatives Risk – Derivatives are financial contracts whose values are, for example, based on (or "derived" from) traditional securities (such as a stock or bond), assets (such as a commodity like gold or a foreign currency), reference rates (such as LIBOR) or market indices (such as the S&P 500® Index). Derivatives involve special risks and may result in losses or may limit a Portfolio Fund's potential gain from favorable market movements. Derivative strategies often involve leverage, which may exaggerate a loss, potentially causing a Portfolio Fund to lose more money than it would have lost had it invested in the underlying security or other asset. The values of derivatives may move in unexpected ways, especially in unusual market conditions, and may result in increased volatility, among other consequences. The use of derivatives may also increase the amount of taxes payable by shareholders holding shares in a taxable account. Other risks arise from a Portfolio Fund's potential inability to terminate or to sell derivative positions. A liquid secondary market may not always exist for the Portfolio Fund's derivative positions at times when the Portfolio Fund might wish to terminate or to sell such positions. Over-the-counter instruments (investments not traded on an exchange) may be illiquid, and transactions in derivatives traded in the over-the-counter market are subject to the risk that the other party will not meet its obligations. The use of derivatives also involves the risks of mispricing or improper valuation and that changes in the value of the derivative may not correlate perfectly with the underlying security, asset, reference rate or index. A Portfolio Fund also may not be able to find a suitable derivative transaction counterparty, and thus may be unable to engage in derivative transactions when it is deemed favorable to do so, or at all. U.S. federal legislation has recently been enacted that provides for new clearing, margin, reporting and registration requirements for participants in the derivatives market. While the ultimate impact is not yet clear, these changes could restrict and/or impose significant costs or other burdens upon the Fund's participation in derivatives transactions. For more information on the risks of derivative investments and strategies, see the Statement of Additional Information.

• Convertible Securities Risk – Certain Portfolio Funds invest in convertible securities, which are subject to the usual risks associated with debt securities, such as interest rate risk and credit risk. Convertible securities also react to changes in the value of the common stock into which they convert. Because the value of a convertible security can be influenced by both interest rates and the common stock's market movements, a convertible security generally is not as sensitive to interest rates as a similar debt security, and generally will not vary in value in response to other factors to the same extent as the underlying common stock. In the event of a liquidation of the issuing company, holders of convertible securities would typically be paid before the company's common stockholders but after holders of any senior debt obligations of the company. A Portfolio Fund may be forced to convert a convertible security before it otherwise would choose to do so, which may decrease the Portfolio Fund's return.

• Non-Diversified Mutual Fund Risk – If a Portfolio Fund is non-diversified, that Portfolio Fund generally may invest a greater percentage of its total assets in the securities of fewer issuers than may a "diversified" fund. This increases the risk that a change in the value of any one investment held by the non-diversified Portfolio Fund could affect the overall value of the Portfolio Fund more than it would affect that of a diversified fund holding a greater number of investments. Accordingly, a non-diversified Portfolio Fund's value will likely be more volatile than the value of more diversified funds. A Portfolio Fund that is non-diversified may not operate as a non-diversified fund at all times.

• Technology Sector Risk – Companies in the technology sector are subject to significant competitive pressures, such as aggressive pricing of their products or services, new market entrants, competition for market share, short product cycles due to an accelerated rate of technological developments and the potential for limited earnings and/or falling profit margins. These companies also face the risks that new services, equipment or technologies will not be accepted by consumers and businesses or will become rapidly obsolete. These factors can affect the profitability of technology companies and, as a result, the value of their securities. Also, patent protection is integral to the success of many companies in the technology sector, and profitability can be affected materially by, among other things, the cost of obtaining (or failing to obtain) patent approvals, the cost of litigating patent infringement and the loss of patent protection for products (which significantly increases pricing pressures and can materially reduce profitability with respect to such products). In addition, many technology companies have limited operating histories. Prices of these companies' securities historically have been more volatile than other securities, especially over the short term. Because certain Portfolio Funds invest a significant portion of their net assets in the equity securities of technology companies, a Portfolio Fund's price may be more volatile than a fund that is invested in a more diverse range of market sectors.

• Health Care Sector Risk - Companies in the health care sector are subject to extensive government regulation. Their profitability can be affected significantly and adversely by restrictions on government reimbursement for medical expenses, government approval of medical products and services, competitive pricing pressures, an increased emphasis on outpatient and other alternative services and other factors. Patent protection is integral to the success of companies in the health care sector, and profitability can be affected materially by, among other things, the cost of obtaining (or failing to obtain) patent approvals, the cost of litigating patent infringement and the loss of patent protection for medical products (which significantly increases pricing pressures and can materially reduce profitability with respect to such products). Companies in the health care sector also potentially are subject to extensive product liability and other similar litigation. Companies in the health care sector are affected by the rising cost of medical products and services, and the effects of such rising costs can be particularly pronounced for companies that are dependent on a relatively limited number of products or services. Medical products also frequently become obsolete due to industry innovation or other causes. Because certain Portfolio Funds invest a significant portion of their net assets in the equity securities of health care companies, a Portfolio Fund's price may be more volatile than a fund that is invested in a more diverse range of market sectors.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The inception date for the Fund's Class A and Class C shares is March 3, 2003. The returns shown for these share classes include the returns of the Fund's Class Z shares (adjusted to reflect the higher class-related operating expenses of such classes, where applicable) for periods from the inception date of Class Z shares (September 25, 2002) to the inception of these classes. Except for differences in expenses and sales charges (where applicable), these classes of shares have annual returns substantially similar to those of Class Z shares, which are not offered in this prospectus, because all classes of the Fund's shares invest in the same portfolio of securities.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class A shares has varied from year to year. These returns do not reflect deductions of sales charges, if any, paid by investors and would be lower if they did.

Year by Year Total Return (%) as of December 31 Each Year

^[1]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    19.22%

Worst:   4th quarter 2008:   -19.26%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns for each period with those of the S&P 500® Index, the Fund's primary benchmark for equity securities, the Barclays U.S. Aggregate Bond Index, the Fund's primary benchmark for debt securities, the Lipper Flexible Portfolio Funds Index and a 50/50 Blended Benchmark. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. The Barclays U.S. Aggregate Bond Index is a market value-weighted index that tracks the daily price, coupon, pay-downs, and total return performance of fixed-rate, publicly placed, dollar-denominated, and non-convertible investment grade debt issues with at least $250 million par amount outstanding and with at least one year to final maturity. The Lipper Flexible Portfolio Funds Index is an equal-weighted index of the 30 largest mutual funds within the Flexible Portfolio fund classification, as defined by Lipper, and shows how the Fund's performance compares with the returns of an index of funds with similar investment objectives. The 50/50 Blended Benchmark was established by the Investment Manager to show how the Fund's performance compares to an equally weighted custom composite of the Fund's primary equity and primary debt benchmarks, the S&P 500® Index and the Barclays U.S. Aggregate Bond Index, respectively. The percentage of the Fund's assets allocated to underlying stock and bond Portfolio Funds will vary, and accordingly the composition of the Fund's portfolio will not always reflect the composition of the 50/50 Blended Benchmark.

Average Annual Total Returns (Columbia Thermostat Fund) (Columbia Thermostat Fund A&C)	Inception Date	1 Year	5 Years	Life of Fund
Class A Shares	Sep. 25, 2002	(1.41%)	2.74%	6.56%
Class A Shares returns after taxes on distributions	Sep. 25, 2002	(2.31%)	1.77%	5.42%
Class A Shares returns after taxes on distributions and sale of Fund shares	Sep. 25, 2002	(0.92%)	1.85%	5.18%
Class C Shares	Sep. 25, 2002	2.87%	3.19%	6.45%
S&P 500® Index (reflects no deductions for fees, expenses or taxes)	Sep. 25, 2002	2.11%	(0.25%)	6.85%
Barclays U.S. Aggregate Bond Index (reflects no deductions for fees, expenses or taxes)	Sep. 25, 2002	7.84%	6.50%	5.33%
Lipper Flexible Portfolio Funds Index (reflects no deductions for taxes)	Sep. 25, 2002	(1.16%)	2.02%	7.10%
50-50 S&P 500/Barclays Capital Aggregate Bond (an equally weighted custom composite of the Fund's primary benchmarks for equity and debt securities, established by the Investment Manager; reflects no deductions for fees, expenses or taxes)	Sep. 25, 2002	5.28%	3.54%	6.43%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown only for Class A shares and will vary for other share classes.

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

[1] Contingent deferred sales charges (CDSC) on certain investments of between $1 million and $50 million redeemed within 18 months of purchase, charged as follows: 1.00% CDSC if redeemed within 12 months of purchase, and 0.50% CDSC if redeemed more than 12, but less than 18, months of purchase, with certain limited exceptions.

[2] This charge applies to investors who buy Class C shares and redeem them within one year of purchase, with certain limited exceptions.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[2] Total annual Fund operating expenses include the annualized average weighted fees and expenses of acquired funds (underlying Portfolio Funds). As a result, the amount shown is higher than the ratio of expenses to average net assets included in Financial Highlights, which reflects only those expenses paid directly by the Fund.

[3] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that ordinary operating expenses (excluding distribution and service fees, interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies) do not exceed the annual rate of 0.25% of the Fund's average daily net assets, through April 30, 2013. The figure shown here is the amount of expected waivers and/or reimbursements. This fee and expense arrangement may only be modified or amended with approval from all parties to such arrangement, including the Fund and the Investment Manager.

[1] Year-to-date return as of March 31, 2012: 8.19%

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(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds. More information about these and other discounts is available from your financial advisor, in the Choosing a Share Class section beginning on page 17 of this prospectus and in Appendix D to the Statement of Additional Information under Sales Charge Waivers beginning on page D-1.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn Fund A,C & I) (Columbia Acorn Fund)	Class A Shares		Class C Shares		Class I Shares
Maximum sales charge (load) imposed on purchases, as a % of offering price	5.75%
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[1]	1.00%	[2]

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn Fund A,C & I) (Columbia Acorn Fund)		Class A Shares	Class C Shares	Class I Shares
Management fees		0.64%	0.64%	0.64%
Distribution and/or service (Rule 12b-1) fees		0.25%	1.00%	none
Other expenses	[1]	0.22%	0.30%	0.07%
Total annual Fund operating expenses		1.11%	1.94%	0.71%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class A, Class C or Class I shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn Fund) (Columbia Acorn Fund A,C & I) (USD $)	1 Year	3 Years	5 Years	10 Years
Class A Shares	682	908	1,151	1,849
Class C Shares	297	609	1,047	2,264
Class I Shares	73	227	395	883

Expense Example, No Redemption (Columbia Acorn Fund) (USD $)	1 Year	3 Years	5 Years	10 Years
Class C Shares (Columbia Acorn Fund A,C & I)	197	609	1,047	2,264

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 18% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion. Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Brazil).

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment. Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The inception date for the Fund's Class I shares is September 27, 2010. The returns shown for Class I shares include the returns of the Fund's Class Z shares for periods prior to the inception date of Class I shares. Except for differences in expenses, Class I shares have annual returns substantially similar to those of Class Z shares, which are not offered in this prospectus, because all classes of the Fund's shares invest in the same portfolio of securities.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class A shares has varied from year to year. These returns do not reflect deductions of sales charges, if any, paid by investors and would be lower if they did.

Year by Year Total Return (%) as of December 31 Each Year

^[1]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    20.87%

Worst:   4th quarter 2008:   -25.19%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns for each period with those of the Russell 2500 Index, the Fund's primary benchmark, the Standard & Poor's (S&P) 500® Index and the Russell 2000 Index. The Russell 2500 Index measures the performance of the 2,500 smallest companies in the Russell 3000 Index, which represents approximately 17% of the total market capitalization of the Russell 3000 Index. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in small and mid-sized companies, the comparison to the S&P 500® Index is presented to show performance against a widely recognized market index. The Russell 2000 Index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index. The Russell 2000 Index shows how the Fund's performance compares to a widely recognized broad based index of companies with somewhat lower capitalization than the Fund's primary benchmark.

Average Annual Total Returns (Columbia Acorn Fund) (Columbia Acorn Fund A,C & I)	1 Year	5 Years	10 Years
Class A Shares	(10.36%)	0.62%	7.21%
Class A Shares returns after taxes on distributions	(10.94%)	0.10%	6.65%
Class A Shares returns after taxes on distributions and sale of Fund shares	(5.94%)	0.53%	6.32%
Class C Shares	(6.53%)	1.02%	7.04%
Class I Shares	(4.57%)	2.14%	8.25%
Russell 2500 Index (reflects no deductions for fees, expenses or taxes)	(2.51%)	1.24%	6.57%
S&P 500® Index (reflects no deductions for fees, expenses or taxes)	2.11%	(0.25%)	2.92%
Russell 2000 Index (reflects no deductions for fees, expenses or taxes)	(4.18%)	0.15%	5.62%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown only for Class A shares and will vary for other share classes.

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn Fund B) | (Columbia Acorn Fund)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn Fund)		Class B Shares (Columbia Acorn Fund B)
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	[1]	5.00%

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn Fund)		Class B Shares (Columbia Acorn Fund B)
Management fees		0.64%
Distribution and/or service (Rule 12b-1) fees		0.75%
Other expenses	[1]	0.42%
Total annual Fund operating expenses		1.81%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class B shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn Fund) (USD $)	1 Year	3 Years	5 Years	10 Years
Class B Shares (Columbia Acorn Fund B)	684	869	1,180	1,943

Expense Example, No Redemption (Columbia Acorn Fund) (USD $)	1 Year	3 Years	5 Years	10 Years
Class B Shares (Columbia Acorn Fund B)	184	569	980	1,943

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 18% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion. Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Brazil).

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class B shares has varied from year to year.

Year by Year Total Return (%) as of December 31 Each Year

^[2]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    20.64%

Worst:   4th quarter 2008:   -25.33%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns for each period with those of the Russell 2500 Index, the Fund's primary benchmark, the Standard & Poor's (S&P) 500® Index and the Russell 2000 Index. The Russell 2500 Index measures the performance of the 2,500 smallest companies in the Russell 3000 Index, which represents approximately 17% of the total market capitalization of the Russell 3000 Index. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in small and mid-sized companies, the comparison to the S&P 500® Index is presented to show performance against a widely recognized market index. The Russell 2000 Index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index. The Russell 2000 Index shows how the Fund's performance compares to a widely recognized broad based index of companies with somewhat lower capitalization than the Fund's primary benchmark.

Average Annual Total Returns (Columbia Acorn Fund) (Columbia Acorn Fund B)	1 Year	5 Years	10 Years
Class B Shares	(9.86%)	0.89%	7.17%
Class B Shares returns after taxes on distributions	(10.50%)	0.33%	6.59%
Class B Shares returns after taxes on distributions and sale of Fund shares	(5.51%)	0.76%	6.29%
Russell 2500 Index (reflects no deductions for fees, expenses or taxes)	(2.51%)	1.24%	6.57%
S&P 500® Index (reflects no deductions for fees, expenses or taxes)	2.11%	(0.25%)	2.92%
Russell 2000 Index (reflects no deductions for fees, expenses or taxes)	(4.18%)	0.15%	5.62%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn Fund Z) | (Columbia Acorn Fund)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn Fund)	Class Z Shares (Columbia Acorn Fund Z)
Maximum sales charge (load) imposed on purchases, as a % of offering price	none
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn Fund)		Class Z Shares (Columbia Acorn Fund Z)
Management fees		0.64%
Distribution and/or service (Rule 12b-1) fees		none
Other expenses	[1]	0.13%
Total annual Fund operating expenses		0.77%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class Z shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn Fund) (USD $)	1 Year	3 Years	5 Years	10 Years
Class Z Shares (Columbia Acorn Fund Z)	79	246	428	954

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 18% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion. Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Brazil).

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class Z shares has varied from year to year.

Year by Year Total Return (%) as of December 31 Each Year

^[3]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    20.90%

Worst:   4th quarter 2008:   -25.11%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns for each period with those of the Russell 2500 Index, the Fund's primary benchmark, the Standard & Poor's (S&P) 500® Index and the Russell 2000 Index. The Russell 2500 Index measures the performance of the 2,500 smallest companies in the Russell 3000 Index, which represents approximately 17% of the total market capitalization of the Russell 3000 Index. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in small and mid-sized companies, the comparison to the S&P 500® Index is presented to show performance against a widely recognized market index. The Russell 2000 Index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index. The Russell 2000 Index shows how the Fund's performance compares to a widely recognized broad based index of companies with somewhat lower capitalization than the Fund's primary benchmark.

Average Annual Total Returns (Columbia Acorn Fund) (Columbia Acorn Fund Z)	1 Year	5 Years	10 Years
Class Z Shares	(4.61%)	2.12%	8.24%
Class Z Shares returns after taxes on distributions	(5.23%)	1.58%	7.66%
Class Z Shares returns after taxes on distributions and sale of Fund shares	(2.13%)	1.81%	7.25%
Russell 2500 Index (reflects no deductions for fees, expenses or taxes)	(2.51%)	1.24%	6.57%
S&P 500® Index (reflects no deductions for fees, expenses or taxes)	2.11%	(0.25%)	2.92%
Russell 2000 Index (reflects no deductions for fees, expenses or taxes)	(4.18%)	0.15%	5.62%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds. More information about these and other discounts is available from your financial advisor, in the Choosing a Share Class section beginning on page 19 of this prospectus and in Appendix D to the Statement of Additional Information under Sales Charge Waivers beginning on page D-1.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn International A,C,I,R & R5) (Columbia Acorn International)	Class A Shares		Class C Shares		Class I Shares	Class R Shares	Class R5 Shares
Maximum sales charge (load) imposed on purchases, as a % of offering price	5.75%
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[1]	1.00%	[2]

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn International A,C,I,R & R5) (Columbia Acorn International)		Class A Shares		Class C Shares		Class I Shares	Class R Shares	Class R5 Shares
Management fees		0.76%		0.76%		0.76%	0.76%	0.76%
Distribution and/or service (Rule 12b-1) fees		0.25%		1.00%		none	0.50%	none
Other expenses	[1]	0.38%		0.40%		0.10%	0.16%	0.11%
Total annual Fund operating expenses		1.39%		2.16%		0.86%	1.42%	0.87%
Fee waivers and/or reimbursements		(0.04%)	[2]	(0.02%)	[2]	none	none	none
Total annual Fund operating expenses after fee waivers and/or reimbursements		1.35%		2.14%		0.86%	1.42%	0.87%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class A, Class C, Class I, Class R or Class R5 shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn International) (Columbia Acorn International A,C,I,R & R5) (USD $)	1 Year	3 Years	5 Years	10 Years
Class A Shares	705	986	1,288	2,144
Class C Shares	317	674	1,158	2,491
Class I Shares	88	274	477	1,061
Class R Shares	145	449	776	1,702
Class R5 Shares	89	278	482	1,073

Expense Example, No Redemption (Columbia Acorn International) (USD $)	1 Year	3 Years	5 Years	10 Years
Class C Shares (Columbia Acorn International A,C,I,R & R5)	217	674	1,158	2,491

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 32% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 75% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Brazil).

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The inception date for the Fund's Class I shares is September 27, 2010 and the inception date for the Fund's Class R and R5 shares is August 2, 2011. The returns shown for Class I, Class R and Class R5 shares each include the returns of the Fund's Class Z shares (adjusted to reflect the higher class-related operating expenses of such classes, where applicable) for periods prior to the inception date of each class. Except for differences in expenses, these classes of shares each have annual returns substantially similar to those of Class Z shares, which are not offered in this prospectus, because all classes of the Fund's shares invest in the same portfolio of securities.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class A shares has varied from year to year. These returns do not reflect deductions of sales charges, if any, paid by investors and would be lower if they did.

Year by Year Total Return (%) as of December 31 Each Year

^[4]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    33.20%

Worst:   3rd quarter 2008:   -23.79%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns, for each period, with those of the Standard & Poor's (S&P) Global Ex-U.S. Between $500 Million and $5 Billion® Index, the Fund's primary benchmark, the S&P Global Ex-U.S. SmallCap® Index and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Global Ex-U.S. Between $500 Million and $5 Billion® Index is a subset of the broad market selected by the index sponsor that represents the mid- and small-cap developed and emerging markets, excluding the United States. The S&P Global Ex-U.S. SmallCap® Index is an unmanaged index consisting of the bottom 20% of institutionally investable capital of developed and emerging countries, excluding the United States. The performance of the S&P Global Ex-U.S. Small Cap® Index is provided to show how the Fund's performance compares to foreign market performance with a similar geographic distribution and wider market cap range than the Fund's primary benchmark. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund's performance compares to a widely recognized broad based index of foreign market performance.

Average Annual Total Returns (Columbia Acorn International) (Columbia Acorn International A,C,I,R & R5)	1 Year	5 Years	10 Years
Class A Shares	(19.29%)	(1.33%)	9.20%
Class A Shares returns after taxes on distributions	(19.82%)	(1.79%)	8.73%
Class A Shares returns after taxes on distributions and sale of Fund shares	(12.29%)	(1.09%)	8.23%
Class C Shares	(15.85%)	(0.93%)	9.03%
Class I Shares	(14.02%)	0.22%	10.28%
Class R Shares	(14.60%)	(0.42%)	9.58%
Class R5 Shares	(14.07%)	0.19%	10.26%
S&P Global Ex-U.S. Between $500 Million and $5 Billion® Index (reflects no deductions for fees, expenses or taxes)	(16.94%)	(0.58%)	11.10%
S&P Global Ex-U.S. SmallCap® Index (reflects no deductions for fees, expenses or taxes)	(17.40%)	(2.14%)	10.33%
MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)	(12.14%)	(4.72%)	4.67%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown only for Class A shares and will vary for other share classes.

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn International B) | (Columbia Acorn International)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn International)		Class B Shares (Columbia Acorn International B)
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	[1]	5.00%

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn International)		Class B Shares (Columbia Acorn International B)
Management fees		0.76%
Distribution and/or service (Rule 12b-1) fees		0.75%
Other expenses	[1]	0.60%
Total annual Fund operating expenses		2.11%
Fee waivers and/or reimbursements	[2]	(0.03%)
Total annual Fund operating expenses after fee waivers and/or reimbursements		2.08%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class B shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn International) (USD $)	1 Year	3 Years	5 Years	10 Years
Class B Shares (Columbia Acorn International B)	711	958	1,331	2,255

Expense Example, No Redemption (Columbia Acorn International) (USD $)	1 Year	3 Years	5 Years	10 Years
Class B Shares (Columbia Acorn International B)	211	658	1,131	2,255

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 32% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 75% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Brazil).

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class B shares has varied from year to year.

Year by Year Total Return (%) as of December 31 Each Year

^[5]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    32.92%

Worst:   3rd quarter 2008:   -23.87%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns, for each period, with those of the Standard & Poor's (S&P) Global Ex-U.S. Between $500 Million and $5 Billion® Index, the Fund's primary benchmark, the S&P Global Ex-U.S. SmallCap® Index and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Global Ex-U.S. Between $500 Million and $5 Billion® Index is a subset of the broad market selected by the index sponsor that represents the mid- and small-cap developed and emerging markets, excluding the United States. The S&P Global Ex-U.S. SmallCap® Index is an unmanaged index consisting of the bottom 20% of institutionally investable capital of developed and emerging countries, excluding the United States. The performance of the S&P Global Ex-U.S. Small Cap® Index is provided to show how the Fund's performance compares to foreign market performance with a similar geographic distribution and wider market cap range than the Fund's primary benchmark. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund's performance compares to a widely recognized broad based index of foreign market performance.

Average Annual Total Returns (Columbia Acorn International) (Columbia Acorn International B)	1 Year	5 Years	10 Years
Class B Shares	(19.07%)	(1.13%)	9.12%
Class B Shares returns after taxes on distributions	(19.63%)	(1.53%)	8.74%
Class B Shares returns after taxes on distributions and sale of Fund shares	(12.13%)	(0.90%)	8.20%
S&P Global Ex-U.S. Between $500 Million and $5 Billion® Index (reflects no deductions for fees, expenses or taxes)	(16.94%)	(0.58%)	11.10%
S&P Global Ex-U.S. SmallCap® Index (reflects no deductions for fees, expenses or taxes)	(17.40%)	(2.14%)	10.33%
MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)	(12.14%)	(4.72%)	4.67%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn International Z) | (Columbia Acorn International)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn International)	Class Z Shares (Columbia Acorn International Z)
Maximum sales charge (load) imposed on purchases, as a % of offering price	none
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn International)		Class Z Shares (Columbia Acorn International Z)
Management fees		0.76%
Distribution and/or service (Rule 12b-1) fees		none
Other expenses	[1]	0.22%
Total annual Fund operating expenses		0.98%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class Z shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn International) (USD $)	1 Year	3 Years	5 Years	10 Years
Class Z Shares (Columbia Acorn International Z)	100	312	542	1,201

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 32% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 75% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Brazil).

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class Z shares has varied from year to year.

Year by Year Total Return (%) as of December 31 Each Year

^[6]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    33.30%

Worst:   3rd quarter 2008:   -23.68%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns, for each period, with those of the Standard & Poor's (S&P) Global Ex-U.S. Between $500 Million and $5 Billion® Index, the Fund's primary benchmark, the S&P Global Ex-U.S. SmallCap® Index and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Global Ex-U.S. Between $500 Million and $5 Billion® Index is a subset of the broad market selected by the index sponsor that represents the mid- and small-cap developed and emerging markets, excluding the United States. The S&P Global Ex-U.S. SmallCap® Index is an unmanaged index consisting of the bottom 20% of institutionally investable capital of developed and emerging countries, excluding the United States. The performance of the S&P Global Ex-U.S. Small Cap® Index is provided to show how the Fund's performance compares to foreign market performance with a similar geographic distribution and wider market cap range than the Fund's primary benchmark. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund's performance compares to a widely recognized broad based index of foreign market performance.

Average Annual Total Returns (Columbia Acorn International) (Columbia Acorn International Z)	1 Year	5 Years	10 Years
Class Z Shares	(14.06%)	0.20%	10.27%
Class Z Shares returns after taxes on distributions	(14.63%)	(0.32%)	9.71%
Class Z Shares returns after taxes on distributions and sale of Fund shares	(8.88%)	0.20%	9.18%
S&P Global Ex-U.S. Between $500 Million and $5 Billion® Index (reflects no deductions for fees, expenses or taxes)	(16.94%)	(0.58%)	11.10%
S&P Global Ex-U.S. SmallCap® Index (reflects no deductions for fees, expenses or taxes)	(17.40%)	(2.14%)	10.33%
MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)	(12.14%)	(4.72%)	4.67%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn USA A,C & I) | (Columbia Acorn USA)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds. More information about these and other discounts is available from your financial advisor, in the Choosing a Share Class section beginning on page 17 of this prospectus and in Appendix D to the Statement of Additional Information under Sales Charge Waivers beginning on page D-1.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn USA A,C & I) (Columbia Acorn USA)	Class A Shares		Class C Shares		Class I Shares
Maximum sales charge (load) imposed on purchases, as a % of offering price	5.75%
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[1]	1.00%	[2]

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn USA A,C & I) (Columbia Acorn USA)		Class A Shares	Class C Shares	Class I Shares
Management fees		0.86%	0.86%	0.86%
Distribution and/or service (Rule 12b-1) fees		0.25%	1.00%	none
Other expenses	[1]	0.22%	0.32%	0.09%
Total annual Fund operating expenses		1.33%	2.18%	0.95%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class A, Class C or Class I shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn USA) (Columbia Acorn USA A,C & I) (USD $)	1 Year	3 Years	5 Years	10 Years
Class A Shares	703	972	1,262	2,084
Class C Shares	321	682	1,169	2,513
Class I Shares	97	303	525	1,166

Expense Example, No Redemption (Columbia Acorn USA) (USD $)	1 Year	3 Years	5 Years	10 Years
Class C Shares (Columbia Acorn USA A,C & I)	221	682	1,169	2,513

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 20% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 80% of its net assets (plus any borrowings for investment purposes) in U.S. companies.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The inception date for the Fund's Class I shares is September 27, 2010. The returns shown for Class I shares include the returns of the Fund's Class Z shares for periods prior to the inception date of Class I shares. Except for differences in expenses, Class I shares have annual returns substantially similar to those of Class Z shares, which are not offered in this prospectus, because all classes of the Fund's shares invest in the same portfolio of securities.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class A shares has varied from year to year. These returns do not reflect deductions of sales charges, if any, paid by investors and would be lower if they did.

Year by Year Total Return (%) as of December 31 Each Year

^[7]

Best and Worst Quarterly Returns During this Period

Best:    3rd quarter 2009:    23.37%

Worst:   4th quarter 2008:   -27.99%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns for each period with those of the Russell 2000 Index. This index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index.

Average Annual Total Returns (Columbia Acorn USA) (Columbia Acorn USA A,C & I)	1 Year	5 Years	10 Years
Class A Shares	(10.66%)	(0.65%)	5.30%
Class A Shares returns after taxes on distributions	(10.74%)	(0.95%)	5.02%
Class A Shares returns after taxes on distributions and sale of Fund shares	(6.81%)	(0.55%)	4.63%
Class C Shares	(6.86%)	(0.25%)	5.14%
Class I Shares	(4.88%)	0.83%	6.31%
Russell 2000 Index (reflects no deductions for fees, expenses or taxes)	(4.18%)	0.15%	5.62%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown only for Class A shares and will vary for other share classes.

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn USA B) | (Columbia Acorn USA)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn USA)		Class B Shares (Columbia Acorn USA B)
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	[1]	5.00%

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn USA)		Class B Shares (Columbia Acorn USA B)
Management fees		0.86%
Distribution and/or service (Rule 12b-1) fees		0.75%
Other expenses	[1]	0.49%
Total annual Fund operating expenses		2.10%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class B shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn USA) (USD $)	1 Year	3 Years	5 Years	10 Years
Class B Shares (Columbia Acorn USA B)	713	958	1,329	2,234

Expense Example, No Redemption (Columbia Acorn USA) (USD $)	1 Year	3 Years	5 Years	10 Years
Class B Shares (Columbia Acorn USA B)	213	658	1,129	2,234

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 20% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 80% of its net assets (plus any borrowings for investment purposes) in U.S. companies.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class B shares has varied from year to year.

Year by Year Total Return (%) as of December 31 Each Year

^[8]

Best and Worst Quarterly Returns During this Period

Best:    3rd quarter 2009:    23.15%

Worst:   4th quarter 2008:   -28.08%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns for each period with those of the Russell 2000 Index. This index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index.

Average Annual Total Returns (Columbia Acorn USA) (Columbia Acorn USA B)	1 Year	5 Years	10 Years
Class B Shares	(10.36%)	(0.45%)	5.25%
Class B Shares returns after taxes on distributions	(10.46%)	(0.77%)	4.95%
Class B Shares returns after taxes on distributions and sale of Fund shares	(6.60%)	(0.37%)	4.59%
Russell 2000 Index (reflects no deductions for fees, expenses or taxes)	(4.18%)	0.15%	5.62%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn USA Z) | (Columbia Acorn USA)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn USA)	Class Z Shares (Columbia Acorn USA Z)
Maximum sales charge (load) imposed on purchases, as a % of offering price	none
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn USA)		Class Z Shares (Columbia Acorn USA Z)
Management fees		0.86%
Distribution and/or service (Rule 12b-1) fees		none
Other expenses	[1]	0.19%
Total annual Fund operating expenses		1.05%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class Z shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn USA) (USD $)	1 Year	3 Years	5 Years	10 Years
Class Z Shares (Columbia Acorn USA Z)	107	334	579	1,283

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 20% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 80% of its net assets (plus any borrowings for investment purposes) in U.S. companies.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class Z shares has varied from year to year.

Year by Year Total Return (%) as of December 31 Each Year

^[9]

Best and Worst Quarterly Returns During this Period

Best:    3rd quarter 2009:    23.55%

Worst:   4th quarter 2008:   -27.96%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns for each period with those of the Russell 2000 Index. This index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index.

Average Annual Total Returns (Columbia Acorn USA) (Columbia Acorn USA Z)	1 Year	5 Years	10 Years
Class Z Shares	(4.95%)	0.82%	6.30%
Class Z Shares returns after taxes on distributions	(5.04%)	0.52%	6.02%
Class Z Shares returns after taxes on distributions and sale of Fund shares	(3.10%)	0.69%	5.54%
Russell 2000 Index (reflects no deductions for fees, expenses or taxes)	(4.18%)	0.15%	5.62%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn Select A,C & I) | (Columbia Acorn Select)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds. More information about these and other discounts is available from your financial advisor, in the Choosing a Share Class section beginning on page 18 of this prospectus and in Appendix D to the Statement of Additional Information under Sales Charge Waivers beginning on page D-1.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn Select A,C & I) (Columbia Acorn Select)	Class A Shares		Class C Shares		Class I Shares
Maximum sales charge (load) imposed on purchases, as a % of offering price	5.75%
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[1]	1.00%	[2]

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn Select A,C & I) (Columbia Acorn Select)		Class A Shares	Class C Shares	Class I Shares
Management fees		0.82%	0.82%	0.82%
Distribution and/or service (Rule 12b-1) fees		0.25%	1.00%	none
Other expenses	[1]	0.28%	0.35%	0.09%
Total annual Fund operating expenses		1.35%	2.17%	0.91%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class A, Class C or Class I shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn Select) (Columbia Acorn Select A,C & I) (USD $)	1 Year	3 Years	5 Years	10 Years
Class A Shares	705	978	1,272	2,105
Class C Shares	320	679	1,164	2,503
Class I Shares	93	290	504	1,120

Expense Example, No Redemption (Columbia Acorn Select) (USD $)	1 Year	3 Years	5 Years	10 Years
Class C Shares (Columbia Acorn Select A,C & I)	220	679	1,164	2,503

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 21% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of companies with market capitalizations under $20 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $20 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $20 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $20 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $20 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Colombia).

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Fund may also invest in companies that the Investment Manager believes have good operational fundamentals but that the Investment Manager believes are undervalued due to negative investor sentiment related to company-specific or market-related conditions. Investments in turnaround and development stage companies may also be made when the Investment Manager believes potential returns outweigh risks of losses.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Opportunistic Investing Risk - Undervalued securities involve the risk that they may never reach their expected full market value, either because the market fails to recognize the security's intrinsic worth or the expected value was misgauged. Undervalued securities also may decline in price even though the Investment Manager believes they are already undervalued. Turnaround companies may never improve their fundamentals, may take much longer than expected to improve, or may improve much less than expected. Development stage companies could fail to develop and deplete their assets, resulting in large percentage losses.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The inception date for the Fund's Class I shares is September 27, 2010. The returns shown for Class I shares include the returns of the Fund's Class Z shares for periods prior to the inception date of Class I shares. Except for differences in expenses, Class I shares have annual returns substantially similar to those of Class Z shares, which are not offered in this prospectus, because all classes of the Fund's shares invest in the same portfolio of securities.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class A shares has varied from year to year. These returns do not reflect deductions of sales charges, if any, paid by investors and would be lower if they did.

Year by Year Total Return (%) as of December 31 Each Year

^[10]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    28.01%

Worst:   4th quarter 2008:   -30.17%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns for each period with those of the Standard & Poor's (S&P) MidCap 400® Index, the Fund's primary benchmark, and the S&P 500® Index. The S&P MidCap 400® Index is a market value-weighted index that tracks the performance of 400 mid-cap U.S. companies. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in companies with market capitalizations under $20 billion at the time of investment, the comparison to the S&P 500® Index is presented to show performance against a widely recognized market index.

Average Annual Total Returns (Columbia Acorn Select) (Columbia Acorn Select A,C & I)	1 Year	5 Years	10 Years
Class A Shares	(21.43%)	(2.52%)	5.07%
Class A Shares returns after taxes on distributions	(21.83%)	(2.76%)	4.82%
Class A Shares returns after taxes on distributions and sale of Fund shares	(13.89%)	(2.16%)	4.40%
Class C Shares	(18.09%)	(2.15%)	4.89%
Class I Shares	(16.25%)	(1.03%)	6.07%
S&P MidCap 400® Index (reflects no deductions for fees, expenses or taxes)	(1.73%)	3.32%	7.04%
S&P 500® Index (reflects no deductions for fees, expenses or taxes)	2.11%	(0.25%)	2.92%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown only for Class A shares and will vary for other share classes.

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn Select B) | (Columbia Acorn Select)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn Select)		Class B Shares (Columbia Acorn Select B)
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	[1]	5.00%

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn Select)		Class B Shares (Columbia Acorn Select B)
Management fees		0.82%
Distribution and/or service (Rule 12b-1) fees		0.75%
Other expenses	[1]	0.48%
Total annual Fund operating expenses		2.05%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class B shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn Select) (USD $)	1 Year	3 Years	5 Years	10 Years
Class B Shares (Columbia Acorn Select B)	708	943	1,303	2,200

Expense Example, No Redemption (Columbia Acorn Select) (USD $)	1 Year	3 Years	5 Years	10 Years
Class B Shares (Columbia Acorn Select B)	208	643	1,103	2,200

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 21% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of companies with market capitalizations under $20 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $20 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $20 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $20 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $20 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Colombia).

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Fund may also invest in companies that the Investment Manager believes have good operational fundamentals but that the Investment Manager believes are undervalued due to negative investor sentiment related to company-specific or market-related conditions. Investments in turnaround and development stage companies may also be made when the Investment Manager believes potential returns outweigh risks of losses.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Opportunistic Investing Risk - Undervalued securities involve the risk that they may never reach their expected full market value, either because the market fails to recognize the security's intrinsic worth or the expected value was misgauged. Undervalued securities also may decline in price even though the Investment Manager believes they are already undervalued. Turnaround companies may never improve their fundamentals, may take much longer than expected to improve, or may improve much less than expected. Development stage companies could fail to develop and deplete their assets, resulting in large percentage losses.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class B shares has varied from year to year.

Year by Year Total Return (%) as of December 31 Each Year

^[11]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    27.78%

Worst:   4th quarter 2008:   -30.26%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns for each period with those of the Standard & Poor's (S&P) MidCap 400® Index, the Fund's primary benchmark, and the S&P 500® Index. The S&P MidCap 400® Index is a market value-weighted index that tracks the performance of 400 mid-cap U.S. companies. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in companies with market capitalizations under $20 billion at the time of investment, the comparison to the S&P 500® Index is presented to show performance against a widely recognized market index.

Average Annual Total Returns (Columbia Acorn Select) (Columbia Acorn Select B)	1 Year	5 Years	10 Years
Class B Shares	(21.22%)	(2.36%)	5.00%
Class B Shares returns after taxes on distributions	(21.49%)	(2.58%)	4.77%
Class B Shares returns after taxes on distributions and sale of Fund shares	(13.77%)	(2.00%)	4.36%
S&P MidCap 400® Index (reflects no deductions for fees, expenses or taxes)	(1.73%)	3.32%	7.04%
S&P 500® Index (reflects no deductions for fees, expenses or taxes)	2.11%	(0.25%)	2.92%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn Select Z) | (Columbia Acorn Select)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn Select)	Class Z Shares (Columbia Acorn Select Z)
Maximum sales charge (load) imposed on purchases, as a % of offering price	none
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn Select)		Class Z Shares (Columbia Acorn Select Z)
Management fees		0.82%
Distribution and/or service (Rule 12b-1) fees		none
Other expenses	[1]	0.18%
Total annual Fund operating expenses		1.00%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class Z shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn Select) (USD $)	1 Year	3 Years	5 Years	10 Years
Class Z Shares (Columbia Acorn Select Z)	102	318	552	1,225

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 21% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of companies with market capitalizations under $20 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $20 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $20 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $20 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $20 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Colombia).

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Fund may also invest in companies that the Investment Manager believes have good operational fundamentals but that the Investment Manager believes are undervalued due to negative investor sentiment related to company-specific or market-related conditions. Investments in turnaround and development stage companies may also be made when the Investment Manager believes potential returns outweigh risks of losses.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Opportunistic Investing Risk - Undervalued securities involve the risk that they may never reach their expected full market value, either because the market fails to recognize the security's intrinsic worth or the expected value was misgauged. Undervalued securities also may decline in price even though the Investment Manager believes they are already undervalued. Turnaround companies may never improve their fundamentals, may take much longer than expected to improve, or may improve much less than expected. Development stage companies could fail to develop and deplete their assets, resulting in large percentage losses.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class Z shares has varied from year to year.

Year by Year Total Return (%) as of December 31 Each Year

^[12]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    28.11%

Worst:   4th quarter 2008:   -30.14%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns for each period with those of the Standard & Poor's (S&P) MidCap 400® Index, the Fund's primary benchmark, and the S&P 500® Index. The S&P MidCap 400® Index is a market value-weighted index that tracks the performance of 400 mid-cap U.S. companies. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in companies with market capitalizations under $20 billion at the time of investment, the comparison to the S&P 500® Index is presented to show performance against a widely recognized market index.

Average Annual Total Returns (Columbia Acorn Select) (Columbia Acorn Select Z)	1 Year	5 Years	10 Years
Class Z Shares	(16.37%)	(1.07%)	6.05%
Class Z Shares returns after taxes on distributions	(16.87%)	(1.33%)	5.77%
Class Z Shares returns after taxes on distributions and sale of Fund shares	(10.60%)	(0.95%)	5.27%
S&P MidCap 400® Index (reflects no deductions for fees, expenses or taxes)	(1.73%)	3.32%	7.04%
S&P 500® Index (reflects no deductions for fees, expenses or taxes)	2.11%	(0.25%)	2.92%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn International Select A,C & I) | (Columbia Acorn International Select)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds. More information about these and other discounts is available from your financial advisor, in the Choosing a Share Class section beginning on page 18 of this prospectus and in Appendix D to the Statement of Additional Information under Sales Charge Waivers beginning on page D-1.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn International Select A,C & I) (Columbia Acorn International Select)	Class A Shares		Class C Shares		Class I Shares
Maximum sales charge (load) imposed on purchases, as a % of offering price	5.75%
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[1]	1.00%	[2]

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn International Select A,C & I) (Columbia Acorn International Select)		Class A Shares	Class C Shares	Class I Shares
Management fees		0.94%	0.94%	0.94%
Distribution and/or service (Rule 12b-1) fees		0.25%	1.00%	none
Other expenses	[1]	0.43%	0.50%	0.14%
Total annual Fund operating expenses		1.62%	2.44%	1.08%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class A, Class C or Class I shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn International Select) (Columbia Acorn International Select A,C & I) (USD $)	1 Year	3 Years	5 Years	10 Years
Class A Shares	730	1,057	1,406	2,386
Class C Shares	347	761	1,301	2,776
Class I Shares	110	343	595	1,317

Expense Example, No Redemption (Columbia Acorn International Select) (USD $)	1 Year	3 Years	5 Years	10 Years
Class C Shares (Columbia Acorn International Select A,C & I)	247	761	1,301	2,776

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 44% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 65% of its net assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom). The Fund also may invest up to 35% of its total assets in companies in emerging markets (for example, China, India and Brazil). The Fund generally invests in at least three countries other than the United States but may invest up to 25% of its total assets in securities of U.S. issuers.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $25 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $25 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $25 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $25 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $25 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies. The Fund also may invest in larger-sized companies.

The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to invest in a limited number of foreign companies (generally between 40-60), offering the potential to provide above-average growth over time.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The inception date for the Fund's Class I shares is September 27, 2010. The returns shown for Class I shares include the returns of the Fund's Class Z shares for periods prior to the inception date of Class I shares. Except for differences in expenses, Class I shares have annual returns substantially similar to those of Class Z shares, which are not offered in this prospectus, because all classes of the Fund's shares invest in the same portfolio of securities.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class A shares has varied from year to year. These returns do not reflect deductions of sales charges, if any, paid by investors and would be lower if they did.

Year by Year Total Return (%) as of December 31 Each Year

^[13]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    23.32%

Worst:   3rd quarter 2008:   -24.85%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns, for each period, with those of the Standard & Poor's (S&P) Developed Ex-U.S. Between $2 Billion and $10 Billion® Index, the Fund's primary benchmark, and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index is a subset of the broad market selected by the index sponsor that represents the mid-cap developed market excluding the United States. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund's performance compares to a widely recognized broad based index of foreign market performance.

Average Annual Total Returns (Columbia Acorn International Select) (Columbia Acorn International Select A,C & I)	1 Year	5 Years	10 Years
Class A Shares	(15.28%)	(1.13%)	8.20%
Class A Shares returns after taxes on distributions	(15.64%)	(1.47%)	8.04%
Class A Shares returns after taxes on distributions and sale of Fund shares	(9.14%)	(0.86%)	7.38%
Class C Shares	(11.69%)	(0.75%)	8.03%
Class I Shares	(9.68%)	0.43%	9.24%
S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index (reflects no deductions for fees, expenses or taxes)	(14.01%)	(3.06%)	8.41%
MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)	(12.14%)	(4.72%)	4.67%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown only for Class A shares and will vary for other share classes.

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn International Select B) | (Columbia Acorn International Select)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn International Select)		Class B Shares (Columbia Acorn International Select B)
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	[1]	5.00%

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn International Select)		Class B Shares (Columbia Acorn International Select B)
Management fees		0.94%
Distribution and/or service (Rule 12b-1) fees		0.75%
Other expenses	[1]	0.63%
Total annual Fund operating expenses		2.32%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class B shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn International Select) (USD $)	1 Year	3 Years	5 Years	10 Years
Class B Shares (Columbia Acorn International Select B)	735	1,024	1,440	2,481

Expense Example, No Redemption (Columbia Acorn International Select) (USD $)	1 Year	3 Years	5 Years	10 Years
Class B Shares (Columbia Acorn International Select B)	235	724	1,240	2,481

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 44% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 65% of its net assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom). The Fund also may invest up to 35% of its total assets in companies in emerging markets (for example, China, India and Brazil). The Fund generally invests in at least three countries other than the United States but may invest up to 25% of its total assets in securities of U.S. issuers.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $25 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $25 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $25 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $25 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $25 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies. The Fund also may invest in larger-sized companies.

The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to invest in a limited number of foreign companies (generally between 40-60), offering the potential to provide above-average growth over time.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class B shares has varied from year to year.

Year by Year Total Return (%) as of December 31 Each Year

^[14]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    23.09%

Worst:   3rd quarter 2008:   -24.96%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns, for each period, with those of the Standard & Poor's (S&P) Developed Ex-U.S. Between $2 Billion and $10 Billion® Index, the Fund's primary benchmark, and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index is a subset of the broad market selected by the index sponsor that represents the mid-cap developed market excluding the United States. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund's performance compares to a widely recognized broad based index of foreign market performance.

Average Annual Total Returns (Columbia Acorn International Select) (Columbia Acorn International Select B)	1 Year	5 Years	10 Years
Class B Shares	(14.99%)	(0.95%)	8.14%
Class B Shares returns after taxes on distributions	(15.22%)	(1.21%)	8.04%
Class B Shares returns after taxes on distributions and sale of Fund shares	(9.13%)	(0.69%)	7.33%
S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index (reflects no deductions for fees, expenses or taxes)	(14.01%)	(3.06%)	8.41%
MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)	(12.14%)	(4.72%)	4.67%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn International Select Z) | (Columbia Acorn International Select)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn International Select)	Class Z Shares (Columbia Acorn International Select Z)
Maximum sales charge (load) imposed on purchases, as a % of offering price	none
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn International Select)		Class Z Shares (Columbia Acorn International Select Z)
Management fees		0.94%
Distribution and/or service (Rule 12b-1) fees		none
Other expenses	[1]	0.31%
Total annual Fund operating expenses		1.25%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class Z shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn International Select) (USD $)	1 Year	3 Years	5 Years	10 Years
Class Z Shares (Columbia Acorn International Select Z)	127	397	686	1,511

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 44% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 65% of its net assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom). The Fund also may invest up to 35% of its total assets in companies in emerging markets (for example, China, India and Brazil). The Fund generally invests in at least three countries other than the United States but may invest up to 25% of its total assets in securities of U.S. issuers.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $25 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $25 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $25 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $25 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $25 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies. The Fund also may invest in larger-sized companies.

The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to invest in a limited number of foreign companies (generally between 40-60), offering the potential to provide above-average growth over time.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class Z shares has varied from year to year.

Year by Year Total Return (%) as of December 31 Each Year

^[15]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    23.44%

Worst:   3rd quarter 2008:   -24.76%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns, for each period, with those of the Standard & Poor's (S&P) Developed Ex-U.S. Between $2 Billion and $10 Billion® Index, the Fund's primary benchmark, and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index is a subset of the broad market selected by the index sponsor that represents the mid-cap developed market excluding the United States. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund's performance compares to a widely recognized broad based index of foreign market performance.

Average Annual Total Returns (Columbia Acorn International Select) (Columbia Acorn International Select Z)	1 Year	5 Years	10 Years
Class Z Shares	(9.76%)	0.41%	9.22%
Class Z Shares returns after taxes on distributions	(10.24%)	0.01%	9.02%
Class Z Shares returns after taxes on distributions and sale of Fund shares	(5.37%)	0.45%	8.31%
S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index (reflects no deductions for fees, expenses or taxes)	(14.01%)	(3.06%)	8.41%
MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)	(12.14%)	(4.72%)	4.67%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Thermostat Fund A&C) | (Columbia Thermostat Fund)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds. More information about these and other discounts is available from your financial advisor, in the Choosing a Share Class section beginning on page 28 of this prospectus and in Appendix D to the Statement of Additional Information under Sales Charge Waivers beginning on page D-1.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Thermostat Fund A&C) (Columbia Thermostat Fund)	Class A Shares		Class C Shares
Maximum sales charge (load) imposed on purchases, as a % of offering price	5.75%
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[1]	1.00%	[2]

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Thermostat Fund A&C) (Columbia Thermostat Fund)		Class A Shares	Class C Shares
Management fees		0.10%	0.10%
Distribution and/or service (Rule 12b-1) fees		0.25%	1.00%
Other expenses	[1]	0.46%	0.46%
Acquired Fund Fees and Expenses		0.65%	0.65%
Total annual Fund operating expenses	[2]	1.46%	2.21%
Fee waivers and/or reimbursements	[3]	(0.31%)	(0.31%)
Total annual Fund operating expenses after fee waivers and/or reimbursements		1.15%	1.90%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class A or Class C shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire on April 30, 2013, they are only reflected in the 1 year example and the first year of the 3, 5 and 10 year examples.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Thermostat Fund) (Columbia Thermostat Fund A&C) (USD $)	1 Year	3 Years	5 Years	10 Years
Class A Shares	685	981	1,299	2,196
Class C Shares	293	661	1,156	2,520

Expense Example, No Redemption (Columbia Thermostat Fund) (USD $)	1 Year	3 Years	5 Years	10 Years
Class C Shares (Columbia Thermostat Fund A&C)	193	661	1,156	2,520

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund will indirectly bear the expenses associated with portfolio turnover of the underlying Portfolio Funds in which the Fund invests. Each Portfolio Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A Portfolio Fund's higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when its shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 130% of the average value of its portfolio.

Principal Investment Strategies

The Fund pursues its investment objective by investing in other mutual funds. As a "fund of funds," under normal circumstances, the Fund allocates at least 95% of its net assets (stock/bond assets) among a selected group of stock and bond mutual funds (Portfolio Funds) according to the current level of Standard & Poor's (S&P) 500® Index. Generally, when the S&P 500® Index goes up in relation to predetermined ranges set by Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), the Fund sells a portion of its stock funds and invests more in the bond funds and when the S&P 500® Index goes down in relation to the ranges, the Fund increases its investment in the stock funds. Under normal circumstances, the Fund may invest up to 5% of net assets plus any cash received that day in cash, high quality short-term paper and government securities.

Many asset allocation funds typically move assets from stocks to bonds when the market goes up, and from bonds to stocks when the market goes down. Most asset allocation funds are run by sophisticated investment professionals, who make subjective decisions based on economic and financial data and complex graphs of market behavior. By contrast, the day-to-day investment decisions for the Fund are made according to a single predetermined rule. The temperature in your house is run by a single rule: your thermostat turns on the furnace if your house is too cold or turns on the air conditioner if your house is too warm. This Fund works the same way, so it is named Columbia Thermostat Fund.

Because the Fund invests according to a pre-set program, there is no need for subjective day-to-day management. Although another successful asset allocation strategy might do better than the Fund, the Fund is designed for those who doubt the wisdom of trying to "time" the market and are unsure of the long-term trend of the stock market. The Fund takes psychology out of investing; it avoids the temptation to buy more stocks because the stock market is currently going up or to sell stocks because the market is declining. The Fund operates continuously and substantially automatically, subject to periodic review of the pre-set program by the Investment Manager and the Fund's Board of Trustees. As described more fully below, the Investment Manager has the authority to review the structure and allocation ranges of the stock/bond allocation table and to make any changes considered appropriate.

The Investment Manager chooses the Portfolio Funds to provide participation in the major sectors of the stock and bond markets. If you believe that the stock market will tend to go up most of the time, then you should probably own a fully invested stock fund and use a buy-and-hold strategy. Buy-and-hold was an excellent strategy in the 1982-1999 bull market. However, there have been long periods in the past when buy-and-hold was not the best strategy, such as 1930-1954 and 1969-1981, when the market fluctuated but did not make significant new highs. The Fund may be a good investment choice for you if you believe that the market may fluctuate in a trading range for many years, that a remarkable bull market ended early in 2000 and that the market may not reach significant new highs for many years.

The Fund invests its stock/bond assets among the Portfolio Funds according to an asset allocation table. The current allocation table is set forth below.

Stock/Bond Allocation Table

                                      How the Fund will Invest the Stock/Bond Assets

                                      ----------------------------------------------



Level of the S and P 500(R) Index   	    Stock Percentage     Bond Percentage

---------------------------------           ----------------     ---------------

over 1750                                          10%                90%

over 1700 -- 1750                                  15%                85%

over 1650 -- 1700                                  20%                80%

over 1600 -- 1650                                  25%                75%

over 1550 -- 1600                                  30%                70%

over 1500 -- 1550                                  35%                65%

over 1450 -- 1500                                  40%                60%

over 1400 -- 1450                                  45%                55%

over 1350 -- 1400                                  50%                50%

over 1300 -- 1350                                  55%                45%

over 1250 -- 1300                                  60%                40%

over 1200 -- 1250                                  65%                35%

over 1150 -- 1200                                  70%                30%

over 1100 -- 1150                                  75%                25%

over 1050 -- 1100                                  80%                20%

over 1000 -- 1050                                  85%                15%

1000 and under                                     90%                10%

When the S&P 500® Index moves into a new band on the table, the Fund promptly will rebalance the stock/bond mix to reflect the new S&P 500® Index price level by redeeming shares of some Portfolio Funds and purchasing shares of other Portfolio Funds. The only exception will be a "31-day Rule"; in order to reduce taxable events, after the Fund has increased its percentage allocation to either stock funds or bond funds, it will not decrease that allocation for at least 31 days. Following a change in the Fund's stock/bond mix, if the S&P 500® Index remains within the same band for a while, normal market fluctuations will change the values of the Fund's holdings of stock Portfolio Funds and bond Portfolio Funds. The Investment Manager will invest cash flows from sales (or redemptions) of Fund shares to bring the stock/bond mix back toward the allocation percentages for that S&P 500® Index band. For example, if the S&P 500® Index is in the 1150-1200 band, and the value of the holdings of the stock Portfolio Funds has dropped to 68% of the value of the holdings of all Portfolio Funds, the Investment Manager would invest new cash in the stock Portfolio Funds (or cash for redemptions would come from the bond Portfolio Funds). If the 31-day Rule is in effect, the Investment Manager will invest new cash at the stock/bond percentage allocation as of the latest rebalancing.

As an illustrative example, suppose the following:

 		              Level of the 		           How the Fund will invest

Date		          S and P 500(R) Index                       the Stock/Bond Assets

--------        ---------------------------------------         --------------------------------

Nov. 1             We begin when the market is 1380                  50% stocks, 50% bonds

Dec. 1             The S and P 500(R) goes to 1401              rebalance 45% stocks, 55% bonds

Dec. 6           The S and P 500(R) drops back to 1390              no reversal for 31 days

Jan. 2              The S and P 500(R) is at 1352               rebalance 50% stocks, 50% bonds

Jan. 20            The S and P 500(R) drops to 1349             rebalance 55% stocks, 45% bonds



      The market has made a continuation move by going through a second action level,

          not a reversal move, so the 31-day Rule does not apply in this case.



Jan. 30            The S and P 500(R) goes up to 1355               no reversal for 31 days

Feb. 20              The S and P 500(R) is at 1360              rebalance 50% stocks, 50% bonds

The following table shows the seven stock Portfolio Funds and three bond Portfolio Funds that the Fund currently uses in its "fund of funds" structure and the current allocation percentage for each Portfolio Fund within the stock or bond category. As described more fully below, the Investment Manager may substitute or add additional Portfolio Funds at any time, including funds introduced after the date of this prospectus. The allocation percentage within each stock/bond category is achieved by rebalancing the investments within the category whenever the S&P 500® Index moves into a new band on the allocation table, subject to the 31-day Rule described above. The Fund does not liquidate its investment in one Portfolio Fund in order to invest in another Portfolio Fund except in connection with a rebalancing due to a move of the S&P 500® Index into a new band (or due to a change by the Investment Manager in the stock/bond allocation table to the Portfolio Funds or to the relative allocation among them). Until a subsequent rebalancing, the Fund's investments in, and redemptions from, the stock Portfolio Funds or the bond Portfolio Funds are allocated among the Portfolio Funds in a manner that will reduce any deviation of the relative values of the Fund's holdings of the Funds from the allocation percentages shown below.

Allocation of Stock/Bond Assets Within Asset Classes

Stock Funds                                   Type of Fund 	             Allocation

-------------------------------------  ------------------------------------  -----------

Columbia Acorn Fund                    Small/Mid-cap growth                          15%

Columbia Acorn Select                  Mid-cap growth                                10%

Columbia Acorn International           Small/Mid-cap international growth            20%

Columbia Dividend Income Fund          Large-cap value                               20%

Columbia Large Cap Enhanced Core Fund  Large-cap blend                               10%

Columbia Contrarian Core Fund          Large-cap blend                               15%

Columbia Select Large Cap Growth Fund  Large-cap growth                              10%

Total                                                                               100%



Bond Funds                                    Type of Fund 	             Allocation

-------------------------------------  ------------------------------------  -----------

Columbia Intermediate Bond Fund        Intermediate-term bonds                       50%

Columbia Income Opportunities Fund     High-yield bonds                              30%

Columbia U.S. Treasury Index Fund      U.S. Treasury notes/bonds                     20%

Total                                                                               100%

The Investment Manager has the authority to review the Portfolio Funds and the relative stock/bond allocation percentages among them and to make any changes considered appropriate.

Each of the Portfolio Funds is currently managed by the Investment Manager or its affiliates. The Fund does not pay any sales load on its purchases of shares of the Portfolio Funds. On an annual basis, or on an "emergency" basis if necessary, the Investment Manager reviews the structure, allocation percentages and Portfolio Funds and makes any changes considered appropriate. The Investment Manager typically addresses the following questions:

• Should the stock/bond allocation table be revised (perhaps because the stock market has made a long-term move outside of the bands set forth above)?
• Should there be a change in the Portfolio Funds or should there be a change in the percentage allocations among the stock/bond funds (perhaps because of a change of portfolio managers, change of investment style, change in relative valuation or a reorganization of a Portfolio Fund)?

Any such changes by the Investment Manager are expected to be infrequent.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Allocation Risk – The Fund uses an asset allocation strategy in pursuit of its investment objective. There is a risk that the Fund's allocation among asset classes or investments will cause the Fund's shares to lose value or cause the Fund to underperform other funds with similar investment objectives, or that the investments themselves will not produce the returns expected.

• Investing in Other Funds Risk – The performance of the underlying fund(s) in which the Fund invests could be adversely affected if other entities that invest in the same underlying fund(s) make relatively large investments or redemptions in the underlying fund(s). In addition, because the expenses and costs of the underlying fund(s) are shared by investors in the underlying fund, redemptions by other investors in the underlying fund could result in decreased economies of scale and increased operating expenses for the underlying fund. The Fund, and its shareholders, indirectly bear a portion of the expenses of the underlying fund(s). These transactions might also result in higher brokerage, tax or other costs for the Fund. This risk may be particularly important when one investor owns a substantial portion of any underlying fund. In addition, the Investment Manager has the authority to change the underlying fund(s) in which the Fund invests or to change the percentage of the Fund's investments allocated to each underlying fund. If an underlying fund pays fees to the Investment Manager or its affiliates, such as advisory fees, this could result in the Investment Manager having a potential conflict of interest in selecting the underlying fund(s) in which the Fund invests or in determining the percentage of the Fund's investments allocated to each underlying fund. In addition, the underlying funds are themselves subject to Investment Strategy Risk.

The Fund is subject indirectly to the following risks of the Portfolio Funds:

• Market Risk – Market risk refers to the possibility that the market values of securities that a Portfolio Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Portfolio Fund. Accordingly, an investment in a Portfolio Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Portfolio Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Interest Rate Risk – Debt securities are subject to interest rate risk. In general, if prevailing interest rates rise, the values of debt securities will tend to fall, and if interest rates fall, the values of debt securities will tend to rise. Changes in the value of a debt security usually will not affect the amount of income a Portfolio Fund receives from it but may affect the value of the Portfolio Fund's shares. Interest rate risk is generally greater for debt securities with longer maturities/durations.

• Credit Risk – Credit risk applies to most debt securities, but is generally less of a factor for obligations backed by the "full faith and credit" of the U.S. Government. A Portfolio Fund could lose money if the issuer of a debt security owned by the Fund is unable or perceived to be unable to pay interest or repay principal when it becomes due. Various factors could affect the issuer's actual or perceived willingness or ability to make timely interest or principal payments, including changes in the issuer's financial condition or in general economic conditions. Debt securities backed by an issuer's taxing authority may be subject to legal limits on the issuer's power to increase taxes or otherwise to raise revenue, or may be dependent on legislative appropriation or government aid. Certain debt securities are backed only by revenues derived from a particular project or source, rather than by an issuer's taxing authority, and thus may have a greater risk of default.

• Low and Below Investment Grade Securities Risk – Debt securities with the lowest investment grade rating (e.g., BBB by Standard & Poor's, a division of the McGraw-Hill Companies, Inc. (S&P), or Fitch, Inc. (Fitch) or Baa by Moody's Investors Service, Inc. (Moody's)), or that are below investment grade (which are commonly referred to as "junk bonds") (e.g., BB or below by S&P or Fitch or Ba by Moody's) and unrated securities of comparable quality are more speculative than securities with higher ratings and may experience greater price fluctuations. These securities tend to be more sensitive to credit risk than higher-rated securities, particularly during a downturn in the economy, which is more likely to weaken the ability of the issuers to make principal and interest payments on these securities. These securities typically pay a premium – a higher interest rate or yield – because of the increased risk of loss, including default. These securities also are generally less liquid than higher-rated securities. The securities ratings provided by Moody's, S&P and Fitch are based on analyses by these ratings agencies of the credit quality of the securities and may not take into account every risk related to whether interest or principal will be timely repaid.

• Value Securities Risk – Value securities are securities of companies that may have experienced, for example, adverse business, industry or other developments or may be subject to special risks that have caused the securities to be out of favor and, in turn, potentially undervalued. The market value of a portfolio security may not meet the Investment Manager's future value assessment of that security, or may decline. There is also a risk that it may take longer than expected for the value of these investments to rise to the believed value. In addition, value securities, at times, may not perform as well as growth securities or the stock market in general, and may be out of favor with investors for varying periods of time.

• Growth Securities Risk – Because growth securities typically trade at a higher multiple of earnings than other types of securities, the market values of growth securities may be more sensitive to changes in current or expected earnings than the market values of other types of securities. In addition, growth securities, at times, may not perform as well as value securities or the stock market in general, and may be out of favor with investors for varying periods of time.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Portfolio Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Portfolio Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Index Risk – U.S. Treasury Index Fund's value will generally decline when the performance of its targeted index declines. Because U.S. Treasury Index Fund is designed to track an index before fees and expenses, U.S. Treasury Index Fund cannot purchase other securities that may help offset declines in its index. In addition, because U.S. Treasury Index Fund may not hold all issues included in its index, may not always be fully invested, and bears advisory, administrative and other expenses and transaction costs in trading securities, U.S. Treasury Index Fund's performance may fail to match the performance of its targeted index, after taking expenses into account. It is not possible to invest directly in an index.

• U.S. Government Obligations Risk – While U.S. Treasury obligations are backed by the "full faith and credit" of the U.S. Government, such securities are nonetheless subject to credit risk (i.e., the risk that the U.S. Government may be, or may be perceived to be, unable or unwilling to honor its financial obligations, such as making payments). Securities issued or guaranteed by federal agencies or authorities and U.S. Government-sponsored instrumentalities or enterprises may or may not be backed by the full faith and credit of the U.S. Government. For example, securities issued by the Federal Home Loan Mortgage Corporation, the Federal National Mortgage Association and the Federal Home Loan Banks are neither insured nor guaranteed by the U.S. Government. These securities may be supported by the ability to borrow from the U.S. Treasury or only by the credit of the issuing agency, authority, instrumentality or enterprise and, as a result, are subject to greater credit risk than securities issued or guaranteed by the U.S. Treasury. Securities guaranteed by the Federal Deposit Insurance Corporation under its Temporary Liquidity Guarantee Program (TLGP) are subject to certain risks, including whether such securities will continue to trade in line with recent experience in relation to treasury and government agency securities in terms of yield spread and the volatility of such spread, as well as uncertainty as to how such securities will trade in the secondary market and whether that market will be liquid or illiquid. The TLGP is subject to change. See ABOUT THE FUNDS' INVESTMENTS - U.S. Government and Related Obligations in the Statement of Additional Information for more information.

• Derivatives Risk – Derivatives are financial contracts whose values are, for example, based on (or "derived" from) traditional securities (such as a stock or bond), assets (such as a commodity like gold or a foreign currency), reference rates (such as LIBOR) or market indices (such as the S&P 500® Index). Derivatives involve special risks and may result in losses or may limit a Portfolio Fund's potential gain from favorable market movements. Derivative strategies often involve leverage, which may exaggerate a loss, potentially causing a Portfolio Fund to lose more money than it would have lost had it invested in the underlying security or other asset. The values of derivatives may move in unexpected ways, especially in unusual market conditions, and may result in increased volatility, among other consequences. The use of derivatives may also increase the amount of taxes payable by shareholders holding shares in a taxable account. Other risks arise from a Portfolio Fund's potential inability to terminate or to sell derivative positions. A liquid secondary market may not always exist for the Portfolio Fund's derivative positions at times when the Portfolio Fund might wish to terminate or to sell such positions. Over-the-counter instruments (investments not traded on an exchange) may be illiquid, and transactions in derivatives traded in the over-the-counter market are subject to the risk that the other party will not meet its obligations. The use of derivatives also involves the risks of mispricing or improper valuation and that changes in the value of the derivative may not correlate perfectly with the underlying security, asset, reference rate or index. A Portfolio Fund also may not be able to find a suitable derivative transaction counterparty, and thus may be unable to engage in derivative transactions when it is deemed favorable to do so, or at all. U.S. federal legislation has recently been enacted that provides for new clearing, margin, reporting and registration requirements for participants in the derivatives market. While the ultimate impact is not yet clear, these changes could restrict and/or impose significant costs or other burdens upon the Fund's participation in derivatives transactions. For more information on the risks of derivative investments and strategies, see the Statement of Additional Information.

• Convertible Securities Risk – Certain Portfolio Funds invest in convertible securities, which are subject to the usual risks associated with debt securities, such as interest rate risk and credit risk. Convertible securities also react to changes in the value of the common stock into which they convert. Because the value of a convertible security can be influenced by both interest rates and the common stock's market movements, a convertible security generally is not as sensitive to interest rates as a similar debt security, and generally will not vary in value in response to other factors to the same extent as the underlying common stock. In the event of a liquidation of the issuing company, holders of convertible securities would typically be paid before the company's common stockholders but after holders of any senior debt obligations of the company. A Portfolio Fund may be forced to convert a convertible security before it otherwise would choose to do so, which may decrease the Portfolio Fund's return.

• Non-Diversified Mutual Fund Risk – If a Portfolio Fund is non-diversified, that Portfolio Fund generally may invest a greater percentage of its total assets in the securities of fewer issuers than may a "diversified" fund. This increases the risk that a change in the value of any one investment held by the non-diversified Portfolio Fund could affect the overall value of the Portfolio Fund more than it would affect that of a diversified fund holding a greater number of investments. Accordingly, a non-diversified Portfolio Fund's value will likely be more volatile than the value of more diversified funds. A Portfolio Fund that is non-diversified may not operate as a non-diversified fund at all times.

• Technology Sector Risk – Companies in the technology sector are subject to significant competitive pressures, such as aggressive pricing of their products or services, new market entrants, competition for market share, short product cycles due to an accelerated rate of technological developments and the potential for limited earnings and/or falling profit margins. These companies also face the risks that new services, equipment or technologies will not be accepted by consumers and businesses or will become rapidly obsolete. These factors can affect the profitability of technology companies and, as a result, the value of their securities. Also, patent protection is integral to the success of many companies in the technology sector, and profitability can be affected materially by, among other things, the cost of obtaining (or failing to obtain) patent approvals, the cost of litigating patent infringement and the loss of patent protection for products (which significantly increases pricing pressures and can materially reduce profitability with respect to such products). In addition, many technology companies have limited operating histories. Prices of these companies' securities historically have been more volatile than other securities, especially over the short term. Because certain Portfolio Funds invest a significant portion of their net assets in the equity securities of technology companies, a Portfolio Fund's price may be more volatile than a fund that is invested in a more diverse range of market sectors.

• Health Care Sector Risk - Companies in the health care sector are subject to extensive government regulation. Their profitability can be affected significantly and adversely by restrictions on government reimbursement for medical expenses, government approval of medical products and services, competitive pricing pressures, an increased emphasis on outpatient and other alternative services and other factors. Patent protection is integral to the success of companies in the health care sector, and profitability can be affected materially by, among other things, the cost of obtaining (or failing to obtain) patent approvals, the cost of litigating patent infringement and the loss of patent protection for medical products (which significantly increases pricing pressures and can materially reduce profitability with respect to such products). Companies in the health care sector also potentially are subject to extensive product liability and other similar litigation. Companies in the health care sector are affected by the rising cost of medical products and services, and the effects of such rising costs can be particularly pronounced for companies that are dependent on a relatively limited number of products or services. Medical products also frequently become obsolete due to industry innovation or other causes. Because certain Portfolio Funds invest a significant portion of their net assets in the equity securities of health care companies, a Portfolio Fund's price may be more volatile than a fund that is invested in a more diverse range of market sectors.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The inception date for the Fund's Class A and Class C shares is March 3, 2003. The returns shown for these share classes include the returns of the Fund's Class Z shares (adjusted to reflect the higher class-related operating expenses of such classes, where applicable) for periods from the inception date of Class Z shares (September 25, 2002) to the inception of these classes. Except for differences in expenses and sales charges (where applicable), these classes of shares have annual returns substantially similar to those of Class Z shares, which are not offered in this prospectus, because all classes of the Fund's shares invest in the same portfolio of securities.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class A shares has varied from year to year. These returns do not reflect deductions of sales charges, if any, paid by investors and would be lower if they did.

Year by Year Total Return (%) as of December 31 Each Year

^[16]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    19.22%

Worst:   4th quarter 2008:   -19.26%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns for each period with those of the S&P 500® Index, the Fund's primary benchmark for equity securities, the Barclays U.S. Aggregate Bond Index, the Fund's primary benchmark for debt securities, the Lipper Flexible Portfolio Funds Index and a 50/50 Blended Benchmark. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. The Barclays U.S. Aggregate Bond Index is a market value-weighted index that tracks the daily price, coupon, pay-downs, and total return performance of fixed-rate, publicly placed, dollar-denominated, and non-convertible investment grade debt issues with at least $250 million par amount outstanding and with at least one year to final maturity. The Lipper Flexible Portfolio Funds Index is an equal-weighted index of the 30 largest mutual funds within the Flexible Portfolio fund classification, as defined by Lipper, and shows how the Fund's performance compares with the returns of an index of funds with similar investment objectives. The 50/50 Blended Benchmark was established by the Investment Manager to show how the Fund's performance compares to an equally weighted custom composite of the Fund's primary equity and primary debt benchmarks, the S&P 500® Index and the Barclays U.S. Aggregate Bond Index, respectively. The percentage of the Fund's assets allocated to underlying stock and bond Portfolio Funds will vary, and accordingly the composition of the Fund's portfolio will not always reflect the composition of the 50/50 Blended Benchmark.

Average Annual Total Returns (Columbia Thermostat Fund) (Columbia Thermostat Fund A&C)	Inception Date	1 Year	5 Years	Life of Fund
Class A Shares	Sep. 25, 2002	(1.41%)	2.74%	6.56%
Class A Shares returns after taxes on distributions	Sep. 25, 2002	(2.31%)	1.77%	5.42%
Class A Shares returns after taxes on distributions and sale of Fund shares	Sep. 25, 2002	(0.92%)	1.85%	5.18%
Class C Shares	Sep. 25, 2002	2.87%	3.19%	6.45%
S&P 500® Index (reflects no deductions for fees, expenses or taxes)	Sep. 25, 2002	2.11%	(0.25%)	6.85%
Barclays U.S. Aggregate Bond Index (reflects no deductions for fees, expenses or taxes)	Sep. 25, 2002	7.84%	6.50%	5.33%
Lipper Flexible Portfolio Funds Index (reflects no deductions for taxes)	Sep. 25, 2002	(1.16%)	2.02%	7.10%
50-50 S&P 500/Barclays Capital Aggregate Bond (an equally weighted custom composite of the Fund's primary benchmarks for equity and debt securities, established by the Investment Manager; reflects no deductions for fees, expenses or taxes)	Sep. 25, 2002	5.28%	3.54%	6.43%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown only for Class A shares and will vary for other share classes.

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Thermostat Fund B) | (Columbia Thermostat Fund)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Thermostat Fund)		Class B Shares (Columbia Thermostat Fund B)
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	[1]	5.00%

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Thermostat Fund)		Class B Shares (Columbia Thermostat Fund B)
Management fees		0.10%
Distribution and/or service (Rule 12b-1) fees		0.75%
Other expenses	[1]	0.52%
Acquired Fund Fees and Expenses		0.65%
Total annual Fund operating expenses	[2]	2.02%
Fee waivers and/or reimbursements	[3]	(0.37%)
Total annual Fund operating expenses after fee waivers and/or reimbursements		1.65%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class B shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire on April 30, 2013, they are only reflected in the 1 year example and the first year of the 3, 5 and 10 year examples.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Thermostat Fund) (USD $)	1 Year	3 Years	5 Years	10 Years
Class B Shares (Columbia Thermostat Fund B)	668	898	1,254	2,174

Expense Example, No Redemption (Columbia Thermostat Fund) (USD $)	1 Year	3 Years	5 Years	10 Years
Class B Shares (Columbia Thermostat Fund B)	168	598	1,054	2,174

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund will indirectly bear the expenses associated with portfolio turnover of the underlying Portfolio Funds in which the Fund invests. Each Portfolio Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A Portfolio Fund's higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when its shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 130% of the average value of its portfolio.

Principal Investment Strategies

The Fund pursues its investment objective by investing in other mutual funds. As a "fund of funds," under normal circumstances, the Fund allocates at least 95% of its net assets (stock/bond assets) among a selected group of stock and bond mutual funds (Portfolio Funds) according to the current level of Standard & Poor's (S&P) 500® Index. Generally, when the S&P 500® Index goes up in relation to predetermined ranges set by Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), the Fund sells a portion of its stock funds and invests more in the bond funds and when the S&P 500® Index goes down in relation to the ranges, the Fund increases its investment in the stock funds. Under normal circumstances, the Fund may invest up to 5% of net assets plus any cash received that day in cash, high quality short-term paper and government securities.

Many asset allocation funds typically move assets from stocks to bonds when the market goes up, and from bonds to stocks when the market goes down. Most asset allocation funds are run by sophisticated investment professionals, who make subjective decisions based on economic and financial data and complex graphs of market behavior. By contrast, the day-to-day investment decisions for the Fund are made according to a single predetermined rule. The temperature in your house is run by a single rule: your thermostat turns on the furnace if your house is too cold or turns on the air conditioner if your house is too warm. This Fund works the same way, so it is named Columbia Thermostat Fund.

Because the Fund invests according to a pre-set program, there is no need for subjective day-to-day management. Although another successful asset allocation strategy might do better than the Fund, the Fund is designed for those who doubt the wisdom of trying to "time" the market and are unsure of the long-term trend of the stock market. The Fund takes psychology out of investing; it avoids the temptation to buy more stocks because the stock market is currently going up or to sell stocks because the market is declining. The Fund operates continuously and substantially automatically, subject to periodic review of the pre-set program by the Investment Manager and the Fund's Board of Trustees. As described more fully below, the Investment Manager has the authority to review the structure and allocation ranges of the stock/bond allocation table and to make any changes considered appropriate.

The Investment Manager chooses the Portfolio Funds to provide participation in the major sectors of the stock and bond markets. If you believe that the stock market will tend to go up most of the time, then you should probably own a fully invested stock fund and use a buy-and-hold strategy. Buy-and-hold was an excellent strategy in the 1982-1999 bull market. However, there have been long periods in the past when buy-and-hold was not the best strategy, such as 1930-1954 and 1969-1981, when the market fluctuated but did not make significant new highs. The Fund may be a good investment choice for you if you believe that the market may fluctuate in a trading range for many years, that a remarkable bull market ended early in 2000 and that the market may not reach significant new highs for many years.

The Fund invests its stock/bond assets among the Portfolio Funds according to an asset allocation table. The current allocation table is set forth below.

Stock/Bond Allocation Table

                                      How the Fund will Invest the Stock/Bond Assets

                                      ----------------------------------------------



Level of the S and P 500(R) Index   	    Stock Percentage     Bond Percentage

---------------------------------           ----------------     ---------------

over 1750                                          10%                90%

over 1700 -- 1750                                  15%                85%

over 1650 -- 1700                                  20%                80%

over 1600 -- 1650                                  25%                75%

over 1550 -- 1600                                  30%                70%

over 1500 -- 1550                                  35%                65%

over 1450 -- 1500                                  40%                60%

over 1400 -- 1450                                  45%                55%

over 1350 -- 1400                                  50%                50%

over 1300 -- 1350                                  55%                45%

over 1250 -- 1300                                  60%                40%

over 1200 -- 1250                                  65%                35%

over 1150 -- 1200                                  70%                30%

over 1100 -- 1150                                  75%                25%

over 1050 -- 1100                                  80%                20%

over 1000 -- 1050                                  85%                15%

1000 and under                                     90%                10%

When the S&P 500® Index moves into a new band on the table, the Fund promptly will rebalance the stock/bond mix to reflect the new S&P 500® Index price level by redeeming shares of some Portfolio Funds and purchasing shares of other Portfolio Funds. The only exception will be a "31-day Rule"; in order to reduce taxable events, after the Fund has increased its percentage allocation to either stock funds or bond funds, it will not decrease that allocation for at least 31 days. Following a change in the Fund's stock/bond mix, if the S&P 500® Index remains within the same band for a while, normal market fluctuations will change the values of the Fund's holdings of stock Portfolio Funds and bond Portfolio Funds. The Investment Manager will invest cash flows from sales (or redemptions) of Fund shares to bring the stock/bond mix back toward the allocation percentages for that S&P 500® Index band. For example, if the S&P 500® Index is in the 1150-1200 band, and the value of the holdings of the stock Portfolio Funds has dropped to 68% of the value of the holdings of all Portfolio Funds, the Investment Manager would invest new cash in the stock Portfolio Funds (or cash for redemptions would come from the bond Portfolio Funds). If the 31-day Rule is in effect, the Investment Manager will invest new cash at the stock/bond percentage allocation as of the latest rebalancing.

As an illustrative example, suppose the following:

 		              Level of the 		           How the Fund will invest

Date		          S and P 500(R) Index                       the Stock/Bond Assets

--------        ---------------------------------------         --------------------------------

Nov. 1             We begin when the market is 1380                  50% stocks, 50% bonds

Dec. 1             The S and P 500(R) goes to 1401              rebalance 45% stocks, 55% bonds

Dec. 6           The S and P 500(R) drops back to 1390              no reversal for 31 days

Jan. 2              The S and P 500(R) is at 1352               rebalance 50% stocks, 50% bonds

Jan. 20            The S and P 500(R) drops to 1349             rebalance 55% stocks, 45% bonds



      The market has made a continuation move by going through a second action level,

          not a reversal move, so the 31-day Rule does not apply in this case.



Jan. 30            The S and P 500(R) goes up to 1355               no reversal for 31 days

Feb. 20              The S and P 500(R) is at 1360              rebalance 50% stocks, 50% bonds

The following table shows the seven stock Portfolio Funds and three bond Portfolio Funds that the Fund currently uses in its "fund of funds" structure and the current allocation percentage for each Portfolio Fund within the stock or bond category. As described more fully below, the Investment Manager may substitute or add additional Portfolio Funds at any time, including funds introduced after the date of this prospectus. The allocation percentage within each stock/bond category is achieved by rebalancing the investments within the category whenever the S&P 500® Index moves into a new band on the allocation table, subject to the 31-day Rule described above. The Fund does not liquidate its investment in one Portfolio Fund in order to invest in another Portfolio Fund except in connection with a rebalancing due to a move of the S&P 500® Index into a new band (or due to a change by the Investment Manager in the stock/bond allocation table to the Portfolio Funds or to the relative allocation among them). Until a subsequent rebalancing, the Fund's investments in, and redemptions from, the stock Portfolio Funds or the bond Portfolio Funds are allocated among the Portfolio Funds in a manner that will reduce any deviation of the relative values of the Fund's holdings of the Funds from the allocation percentages shown below.

Allocation of Stock/Bond Assets Within Asset Classes

Stock Funds                                   Type of Fund 	             Allocation

-------------------------------------  ------------------------------------  -----------

Columbia Acorn Fund                    Small/Mid-cap growth                          15%

Columbia Acorn Select                  Mid-cap growth                                10%

Columbia Acorn International           Small/Mid-cap international growth            20%

Columbia Dividend Income Fund          Large-cap value                               20%

Columbia Large Cap Enhanced Core Fund  Large-cap blend                               10%

Columbia Contrarian Core Fund          Large-cap blend                               15%

Columbia Select Large Cap Growth Fund  Large-cap growth                              10%

Total                                                                               100%



Bond Funds                                    Type of Fund 	             Allocation

-------------------------------------  ------------------------------------  -----------

Columbia Intermediate Bond Fund        Intermediate-term bonds                       50%

Columbia Income Opportunities Fund     High-yield bonds                              30%

Columbia U.S. Treasury Index Fund      U.S. Treasury notes/bonds                     20%

Total                                                                               100%

The Investment Manager has the authority to review the Portfolio Funds and the relative stock/bond allocation percentages among them and to make any changes considered appropriate.

Each of the Portfolio Funds is currently managed by the Investment Manager or its affiliates. The Fund does not pay any sales load on its purchases of shares of the Portfolio Funds. On an annual basis, or on an "emergency" basis if necessary, the Investment Manager reviews the structure, allocation percentages and Portfolio Funds and makes any changes considered appropriate. The Investment Manager typically addresses the following questions:

• Should the stock/bond allocation table be revised (perhaps because the stock market has made a long-term move outside of the bands set forth above)?
• Should there be a change in the Portfolio Funds or should there be a change in the percentage allocations among the stock/bond funds (perhaps because of a change of portfolio managers, change of investment style, change in relative valuation or a reorganization of a Portfolio Fund)?

Any such changes by the Investment Manager are expected to be infrequent.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Allocation Risk – The Fund uses an asset allocation strategy in pursuit of its investment objective. There is a risk that the Fund's allocation among asset classes or investments will cause the Fund's shares to lose value or cause the Fund to underperform other funds with similar investment objectives, or that the investments themselves will not produce the returns expected.

• Investing in Other Funds Risk – The performance of the underlying fund(s) in which the Fund invests could be adversely affected if other entities that invest in the same underlying fund(s) make relatively large investments or redemptions in the underlying fund(s). In addition, because the expenses and costs of the underlying fund(s) are shared by investors in the underlying fund, redemptions by other investors in the underlying fund could result in decreased economies of scale and increased operating expenses for the underlying fund. The Fund, and its shareholders, indirectly bear a portion of the expenses of the underlying fund(s). These transactions might also result in higher brokerage, tax or other costs for the Fund. This risk may be particularly important when one investor owns a substantial portion of any underlying fund. In addition, the Investment Manager has the authority to change the underlying fund(s) in which the Fund invests or to change the percentage of the Fund's investments allocated to each underlying fund. If an underlying fund pays fees to the Investment Manager or its affiliates, such as advisory fees, this could result in the Investment Manager having a potential conflict of interest in selecting the underlying fund(s) in which the Fund invests or in determining the percentage of the Fund's investments allocated to each underlying fund. In addition, the underlying funds are themselves subject to Investment Strategy Risk.

The Fund is subject indirectly to the following risks of the Portfolio Funds:

• Market Risk – Market risk refers to the possibility that the market values of securities that a Portfolio Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Portfolio Fund. Accordingly, an investment in a Portfolio Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Portfolio Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Interest Rate Risk – Debt securities are subject to interest rate risk. In general, if prevailing interest rates rise, the values of debt securities will tend to fall, and if interest rates fall, the values of debt securities will tend to rise. Changes in the value of a debt security usually will not affect the amount of income a Portfolio Fund receives from it but may affect the value of the Portfolio Fund's shares. Interest rate risk is generally greater for debt securities with longer maturities/durations.

• Credit Risk – Credit risk applies to most debt securities, but is generally less of a factor for obligations backed by the "full faith and credit" of the U.S. Government. A Portfolio Fund could lose money if the issuer of a debt security owned by the Fund is unable or perceived to be unable to pay interest or repay principal when it becomes due. Various factors could affect the issuer's actual or perceived willingness or ability to make timely interest or principal payments, including changes in the issuer's financial condition or in general economic conditions. Debt securities backed by an issuer's taxing authority may be subject to legal limits on the issuer's power to increase taxes or otherwise to raise revenue, or may be dependent on legislative appropriation or government aid. Certain debt securities are backed only by revenues derived from a particular project or source, rather than by an issuer's taxing authority, and thus may have a greater risk of default.

• Low and Below Investment Grade Securities Risk – Debt securities with the lowest investment grade rating (e.g., BBB by Standard & Poor's, a division of the McGraw-Hill Companies, Inc. (S&P), or Fitch, Inc. (Fitch) or Baa by Moody's Investors Service, Inc. (Moody's)), or that are below investment grade (which are commonly referred to as "junk bonds") (e.g., BB or below by S&P or Fitch or Ba by Moody's) and unrated securities of comparable quality are more speculative than securities with higher ratings and may experience greater price fluctuations. These securities tend to be more sensitive to credit risk than higher-rated securities, particularly during a downturn in the economy, which is more likely to weaken the ability of the issuers to make principal and interest payments on these securities. These securities typically pay a premium – a higher interest rate or yield – because of the increased risk of loss, including default. These securities also are generally less liquid than higher-rated securities. The securities ratings provided by Moody's, S&P and Fitch are based on analyses by these ratings agencies of the credit quality of the securities and may not take into account every risk related to whether interest or principal will be timely repaid.

• Value Securities Risk – Value securities are securities of companies that may have experienced, for example, adverse business, industry or other developments or may be subject to special risks that have caused the securities to be out of favor and, in turn, potentially undervalued. The market value of a portfolio security may not meet the Investment Manager's future value assessment of that security, or may decline. There is also a risk that it may take longer than expected for the value of these investments to rise to the believed value. In addition, value securities, at times, may not perform as well as growth securities or the stock market in general, and may be out of favor with investors for varying periods of time.

• Growth Securities Risk – Because growth securities typically trade at a higher multiple of earnings than other types of securities, the market values of growth securities may be more sensitive to changes in current or expected earnings than the market values of other types of securities. In addition, growth securities, at times, may not perform as well as value securities or the stock market in general, and may be out of favor with investors for varying periods of time.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Portfolio Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Portfolio Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Index Risk – U.S. Treasury Index Fund's value will generally decline when the performance of its targeted index declines. Because U.S. Treasury Index Fund is designed to track an index before fees and expenses, U.S. Treasury Index Fund cannot purchase other securities that may help offset declines in its index. In addition, because U.S. Treasury Index Fund may not hold all issues included in its index, may not always be fully invested, and bears advisory, administrative and other expenses and transaction costs in trading securities, U.S. Treasury Index Fund's performance may fail to match the performance of its targeted index, after taking expenses into account. It is not possible to invest directly in an index.

• U.S. Government Obligations Risk – While U.S. Treasury obligations are backed by the "full faith and credit" of the U.S. Government, such securities are nonetheless subject to credit risk (i.e., the risk that the U.S. Government may be, or may be perceived to be, unable or unwilling to honor its financial obligations, such as making payments). Securities issued or guaranteed by federal agencies or authorities and U.S. Government-sponsored instrumentalities or enterprises may or may not be backed by the full faith and credit of the U.S. Government. For example, securities issued by the Federal Home Loan Mortgage Corporation, the Federal National Mortgage Association and the Federal Home Loan Banks are neither insured nor guaranteed by the U.S. Government. These securities may be supported by the ability to borrow from the U.S. Treasury or only by the credit of the issuing agency, authority, instrumentality or enterprise and, as a result, are subject to greater credit risk than securities issued or guaranteed by the U.S. Treasury. Securities guaranteed by the Federal Deposit Insurance Corporation under its Temporary Liquidity Guarantee Program (TLGP) are subject to certain risks, including whether such securities will continue to trade in line with recent experience in relation to treasury and government agency securities in terms of yield spread and the volatility of such spread, as well as uncertainty as to how such securities will trade in the secondary market and whether that market will be liquid or illiquid. The TLGP is subject to change. See ABOUT THE FUNDS' INVESTMENTS - U.S. Government and Related Obligations in the Statement of Additional Information for more information.

• Derivatives Risk – Derivatives are financial contracts whose values are, for example, based on (or "derived" from) traditional securities (such as a stock or bond), assets (such as a commodity like gold or a foreign currency), reference rates (such as LIBOR) or market indices (such as the S&P 500® Index). Derivatives involve special risks and may result in losses or may limit a Portfolio Fund's potential gain from favorable market movements. Derivative strategies often involve leverage, which may exaggerate a loss, potentially causing a Portfolio Fund to lose more money than it would have lost had it invested in the underlying security or other asset. The values of derivatives may move in unexpected ways, especially in unusual market conditions, and may result in increased volatility, among other consequences. The use of derivatives may also increase the amount of taxes payable by shareholders holding shares in a taxable account. Other risks arise from a Portfolio Fund's potential inability to terminate or to sell derivative positions. A liquid secondary market may not always exist for the Portfolio Fund's derivative positions at times when the Portfolio Fund might wish to terminate or to sell such positions. Over-the-counter instruments (investments not traded on an exchange) may be illiquid, and transactions in derivatives traded in the over-the-counter market are subject to the risk that the other party will not meet its obligations. The use of derivatives also involves the risks of mispricing or improper valuation and that changes in the value of the derivative may not correlate perfectly with the underlying security, asset, reference rate or index. A Portfolio Fund also may not be able to find a suitable derivative transaction counterparty, and thus may be unable to engage in derivative transactions when it is deemed favorable to do so, or at all. U.S. federal legislation has recently been enacted that provides for new clearing, margin, reporting and registration requirements for participants in the derivatives market. While the ultimate impact is not yet clear, these changes could restrict and/or impose significant costs or other burdens upon the Fund's participation in derivatives transactions. For more information on the risks of derivative investments and strategies, see the Statement of Additional Information.

• Convertible Securities Risk – Certain Portfolio Funds invest in convertible securities, which are subject to the usual risks associated with debt securities, such as interest rate risk and credit risk. Convertible securities also react to changes in the value of the common stock into which they convert. Because the value of a convertible security can be influenced by both interest rates and the common stock's market movements, a convertible security generally is not as sensitive to interest rates as a similar debt security, and generally will not vary in value in response to other factors to the same extent as the underlying common stock. In the event of a liquidation of the issuing company, holders of convertible securities would typically be paid before the company's common stockholders but after holders of any senior debt obligations of the company. A Portfolio Fund may be forced to convert a convertible security before it otherwise would choose to do so, which may decrease the Portfolio Fund's return.

• Non-Diversified Mutual Fund Risk – If a Portfolio Fund is non-diversified, that Portfolio Fund generally may invest a greater percentage of its total assets in the securities of fewer issuers than may a "diversified" fund. This increases the risk that a change in the value of any one investment held by the non-diversified Portfolio Fund could affect the overall value of the Portfolio Fund more than it would affect that of a diversified fund holding a greater number of investments. Accordingly, a non-diversified Portfolio Fund's value will likely be more volatile than the value of more diversified funds. A Portfolio Fund that is non-diversified may not operate as a non-diversified fund at all times.

• Technology Sector Risk – Companies in the technology sector are subject to significant competitive pressures, such as aggressive pricing of their products or services, new market entrants, competition for market share, short product cycles due to an accelerated rate of technological developments and the potential for limited earnings and/or falling profit margins. These companies also face the risks that new services, equipment or technologies will not be accepted by consumers and businesses or will become rapidly obsolete. These factors can affect the profitability of technology companies and, as a result, the value of their securities. Also, patent protection is integral to the success of many companies in the technology sector, and profitability can be affected materially by, among other things, the cost of obtaining (or failing to obtain) patent approvals, the cost of litigating patent infringement and the loss of patent protection for products (which significantly increases pricing pressures and can materially reduce profitability with respect to such products). In addition, many technology companies have limited operating histories. Prices of these companies' securities historically have been more volatile than other securities, especially over the short term. Because certain Portfolio Funds invest a significant portion of their net assets in the equity securities of technology companies, a Portfolio Fund's price may be more volatile than a fund that is invested in a more diverse range of market sectors.

• Health Care Sector Risk - Companies in the health care sector are subject to extensive government regulation. Their profitability can be affected significantly and adversely by restrictions on government reimbursement for medical expenses, government approval of medical products and services, competitive pricing pressures, an increased emphasis on outpatient and other alternative services and other factors. Patent protection is integral to the success of companies in the health care sector, and profitability can be affected materially by, among other things, the cost of obtaining (or failing to obtain) patent approvals, the cost of litigating patent infringement and the loss of patent protection for medical products (which significantly increases pricing pressures and can materially reduce profitability with respect to such products). Companies in the health care sector also potentially are subject to extensive product liability and other similar litigation. Companies in the health care sector are affected by the rising cost of medical products and services, and the effects of such rising costs can be particularly pronounced for companies that are dependent on a relatively limited number of products or services. Medical products also frequently become obsolete due to industry innovation or other causes. Because certain Portfolio Funds invest a significant portion of their net assets in the equity securities of health care companies, a Portfolio Fund's price may be more volatile than a fund that is invested in a more diverse range of market sectors.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The inception date for the Fund's Class B shares is March 3, 2003. The returns shown for this share class include the returns of the Fund's Class Z shares (adjusted to reflect the higher class-related operating expenses of Class B shares) for periods from the inception date of Class Z shares (September 25, 2002) to the inception date of Class B shares. Except for differences in expenses and sales charges, Class B shares have annual returns substantially similar to those of Class Z shares, which are not offered in this prospectus, because all classes of the Fund's shares invest in the same portfolio of securities.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class B shares has varied from year to year.

Year by Year Total Return (%) as of December 31 Each Year

^[17]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    19.07%

Worst:   4th quarter 2008:   -19.47%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns for each period with those of the S&P 500® Index, the Fund's primary benchmark for equity securities, the Barclays U.S. Aggregate Bond Index, the Fund's primary benchmark for debt securities, the Lipper Flexible Portfolio Funds Index and a 50/50 Blended Benchmark. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. The Barclays U.S. Aggregate Bond Index is a market value-weighted index that tracks the daily price, coupon, pay-downs, and total return performance of fixed-rate, publicly placed, dollar-denominated, and non-convertible investment grade debt issues with at least $250 million par amount outstanding and with at least one year to final maturity. The Lipper Flexible Portfolio Funds Index is an equal-weighted index of the 30 largest mutual funds within the Flexible Portfolio fund classification, as defined by Lipper, and shows how the Fund's performance compares with the returns of an index of funds with similar investment objectives. The 50/50 Blended Benchmark was established by the Investment Manager to show how the Fund's performance compares to an equally weighted custom composite of the Fund's primary equity and primary debt benchmarks, the S&P 500® Index and the Barclays U.S. Aggregate Bond Index, respectively. The percentage of the Fund's assets allocated to underlying stock and bond Portfolio Funds will vary, and accordingly the composition of the Fund's portfolio will not always reflect the composition of the 50/50 Blended Benchmark.

Average Annual Total Returns (Columbia Thermostat Fund) (Columbia Thermostat Fund B)	Inception Date	1 Year	5 Years	Life of Fund
Class B Shares	Sep. 25, 2002	(0.81%)	3.10%	6.65%
Class B Shares returns after taxes on distributions	Sep. 25, 2002	(1.53%)	2.27%	5.70%
Class B Shares returns after taxes on distributions and sale of Fund shares	Sep. 25, 2002	(0.53%)	2.24%	5.38%
S&P 500® Index (reflects no deductions for fees, expenses or taxes)	Sep. 25, 2002	2.11%	(0.25%)	6.85%
Barclays U.S. Aggregate Bond Index (reflects no deductions for fees, expenses or taxes)	Sep. 25, 2002	7.84%	6.50%	5.33%
Lipper Flexible Portfolio Funds Index (reflects no deductions for taxes)	Sep. 25, 2002	(1.16%)	2.02%	7.10%
50-50 S&P 500/Barclays Capital Aggregate Bond (an equally weighted custom composite of the Fund's primary benchmarks for equity and debt securities, established by the Investment Manager; reflects no deductions for fees, expenses or taxes)	Sep. 25, 2002	5.28%	3.54%	6.43%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Thermostat Fund Z) | (Columbia Thermostat Fund)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Thermostat Fund)	Class Z Shares (Columbia Thermostat Fund Z)
Maximum sales charge (load) imposed on purchases, as a % of offering price	none
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Thermostat Fund)		Class Z Shares (Columbia Thermostat Fund Z)
Management fees		0.10%
Distribution and/or service (Rule 12b-1) fees		none
Other expenses	[1]	0.28%
Acquired Fund Fees and Expenses		0.65%
Total annual Fund operating expenses	[2]	1.03%
Fee waivers and/or reimbursements	[3]	(0.13%)
Total annual Fund operating expenses after fee waivers and/or reimbursements		0.90%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class Z shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire on April 30, 2013, they are only reflected in the 1 year example and the first year of the 3, 5 and 10 year examples.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Thermostat Fund) (USD $)	1 Year	3 Years	5 Years	10 Years
Class Z Shares (Columbia Thermostat Fund Z)	92	315	556	1,248

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund will indirectly bear the expenses associated with portfolio turnover of the underlying Portfolio Funds in which the Fund invests. Each Portfolio Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A Portfolio Fund's higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when its shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 130% of the average value of its portfolio.

Principal Investment Strategies

The Fund pursues its investment objective by investing in other mutual funds. As a "fund of funds," under normal circumstances, the Fund allocates at least 95% of its net assets (stock/bond assets) among a selected group of stock and bond mutual funds (Portfolio Funds) according to the current level of Standard & Poor's (S&P) 500® Index. Generally, when the S&P 500® Index goes up in relation to predetermined ranges set by Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), the Fund sells a portion of its stock funds and invests more in the bond funds and when the S&P 500® Index goes down in relation to the ranges, the Fund increases its investment in the stock funds. Under normal circumstances, the Fund may invest up to 5% of net assets plus any cash received that day in cash, high quality short-term paper and government securities.

Many asset allocation funds typically move assets from stocks to bonds when the market goes up, and from bonds to stocks when the market goes down. Most asset allocation funds are run by sophisticated investment professionals, who make subjective decisions based on economic and financial data and complex graphs of market behavior. By contrast, the day-to-day investment decisions for the Fund are made according to a single predetermined rule. The temperature in your house is run by a single rule: your thermostat turns on the furnace if your house is too cold or turns on the air conditioner if your house is too warm. This Fund works the same way, so it is named Columbia Thermostat Fund.

Because the Fund invests according to a pre-set program, there is no need for subjective day-to-day management. Although another successful asset allocation strategy might do better than the Fund, the Fund is designed for those who doubt the wisdom of trying to "time" the market and are unsure of the long-term trend of the stock market. The Fund takes psychology out of investing; it avoids the temptation to buy more stocks because the stock market is currently going up or to sell stocks because the market is declining. The Fund operates continuously and substantially automatically, subject to periodic review of the pre-set program by the Investment Manager and the Fund's Board of Trustees. As described more fully below, the Investment Manager has the authority to review the structure and allocation ranges of the stock/bond allocation table and to make any changes considered appropriate.

The Investment Manager chooses the Portfolio Funds to provide participation in the major sectors of the stock and bond markets. If you believe that the stock market will tend to go up most of the time, then you should probably own a fully invested stock fund and use a buy-and-hold strategy. Buy-and-hold was an excellent strategy in the 1982-1999 bull market. However, there have been long periods in the past when buy-and-hold was not the best strategy, such as 1930-1954 and 1969-1981, when the market fluctuated but did not make significant new highs. The Fund may be a good investment choice for you if you believe that the market may fluctuate in a trading range for many years, that a remarkable bull market ended early in 2000 and that the market may not reach significant new highs for many years.

The Fund invests its stock/bond assets among the Portfolio Funds according to an asset allocation table. The current allocation table is set forth below.

Stock/Bond Allocation Table

                                      How the Fund will Invest the Stock/Bond Assets

                                      ----------------------------------------------



Level of the S and P 500(R) Index   	    Stock Percentage     Bond Percentage

---------------------------------           ----------------     ---------------

over 1750                                          10%                90%

over 1700 -- 1750                                  15%                85%

over 1650 -- 1700                                  20%                80%

over 1600 -- 1650                                  25%                75%

over 1550 -- 1600                                  30%                70%

over 1500 -- 1550                                  35%                65%

over 1450 -- 1500                                  40%                60%

over 1400 -- 1450                                  45%                55%

over 1350 -- 1400                                  50%                50%

over 1300 -- 1350                                  55%                45%

over 1250 -- 1300                                  60%                40%

over 1200 -- 1250                                  65%                35%

over 1150 -- 1200                                  70%                30%

over 1100 -- 1150                                  75%                25%

over 1050 -- 1100                                  80%                20%

over 1000 -- 1050                                  85%                15%

1000 and under                                     90%                10%

When the S&P 500® Index moves into a new band on the table, the Fund promptly will rebalance the stock/bond mix to reflect the new S&P 500® Index price level by redeeming shares of some Portfolio Funds and purchasing shares of other Portfolio Funds. The only exception will be a "31-day Rule"; in order to reduce taxable events, after the Fund has increased its percentage allocation to either stock funds or bond funds, it will not decrease that allocation for at least 31 days. Following a change in the Fund's stock/bond mix, if the S&P 500® Index remains within the same band for a while, normal market fluctuations will change the values of the Fund's holdings of stock Portfolio Funds and bond Portfolio Funds. The Investment Manager will invest cash flows from sales (or redemptions) of Fund shares to bring the stock/bond mix back toward the allocation percentages for that S&P 500® Index band. For example, if the S&P 500® Index is in the 1150-1200 band, and the value of the holdings of the stock Portfolio Funds has dropped to 68% of the value of the holdings of all Portfolio Funds, the Investment Manager would invest new cash in the stock Portfolio Funds (or cash for redemptions would come from the bond Portfolio Funds). If the 31-day Rule is in effect, the Investment Manager will invest new cash at the stock/bond percentage allocation as of the latest rebalancing.

As an illustrative example, suppose the following:

 		              Level of the 		           How the Fund will invest

Date		          S and P 500(R) Index                       the Stock/Bond Assets

--------        ---------------------------------------         --------------------------------

Nov. 1             We begin when the market is 1380                  50% stocks, 50% bonds

Dec. 1             The S and P 500(R) goes to 1401              rebalance 45% stocks, 55% bonds

Dec. 6           The S and P 500(R) drops back to 1390              no reversal for 31 days

Jan. 2              The S and P 500(R) is at 1352               rebalance 50% stocks, 50% bonds

Jan. 20            The S and P 500(R) drops to 1349             rebalance 55% stocks, 45% bonds



      The market has made a continuation move by going through a second action level,

          not a reversal move, so the 31-day Rule does not apply in this case.



Jan. 30            The S and P 500(R) goes up to 1355               no reversal for 31 days

Feb. 20              The S and P 500(R) is at 1360              rebalance 50% stocks, 50% bonds

The following table shows the seven stock Portfolio Funds and three bond Portfolio Funds that the Fund currently uses in its "fund of funds" structure and the current allocation percentage for each Portfolio Fund within the stock or bond category. As described more fully below, the Investment Manager may substitute or add additional Portfolio Funds at any time, including funds introduced after the date of this prospectus. The allocation percentage within each stock/bond category is achieved by rebalancing the investments within the category whenever the S&P 500® Index moves into a new band on the allocation table, subject to the 31-day Rule described above. The Fund does not liquidate its investment in one Portfolio Fund in order to invest in another Portfolio Fund except in connection with a rebalancing due to a move of the S&P 500® Index into a new band (or due to a change by the Investment Manager in the stock/bond allocation table to the Portfolio Funds or to the relative allocation among them). Until a subsequent rebalancing, the Fund's investments in, and redemptions from, the stock Portfolio Funds or the bond Portfolio Funds are allocated among the Portfolio Funds in a manner that will reduce any deviation of the relative values of the Fund's holdings of the Funds from the allocation percentages shown below.

Allocation of Stock/Bond Assets Within Asset Classes

Stock Funds                                   Type of Fund 	             Allocation

-------------------------------------  ------------------------------------  -----------

Columbia Acorn Fund                    Small/Mid-cap growth                          15%

Columbia Acorn Select                  Mid-cap growth                                10%

Columbia Acorn International           Small/Mid-cap international growth            20%

Columbia Dividend Income Fund          Large-cap value                               20%

Columbia Large Cap Enhanced Core Fund  Large-cap blend                               10%

Columbia Contrarian Core Fund          Large-cap blend                               15%

Columbia Select Large Cap Growth Fund  Large-cap growth                              10%

Total                                                                               100%



Bond Funds                                    Type of Fund 	             Allocation

-------------------------------------  ------------------------------------  -----------

Columbia Intermediate Bond Fund        Intermediate-term bonds                       50%

Columbia Income Opportunities Fund     High-yield bonds                              30%

Columbia U.S. Treasury Index Fund      U.S. Treasury notes/bonds                     20%

Total                                                                               100%

The Investment Manager has the authority to review the Portfolio Funds and the relative stock/bond allocation percentages among them and to make any changes considered appropriate.

Each of the Portfolio Funds is currently managed by the Investment Manager or its affiliates. The Fund does not pay any sales load on its purchases of shares of the Portfolio Funds. On an annual basis, or on an "emergency" basis if necessary, the Investment Manager reviews the structure, allocation percentages and Portfolio Funds and makes any changes considered appropriate. The Investment Manager typically addresses the following questions:

• Should the stock/bond allocation table be revised (perhaps because the stock market has made a long-term move outside of the bands set forth above)?
• Should there be a change in the Portfolio Funds or should there be a change in the percentage allocations among the stock/bond funds (perhaps because of a change of portfolio managers, change of investment style, change in relative valuation or a reorganization of a Portfolio Fund)?

Any such changes by the Investment Manager are expected to be infrequent.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Allocation Risk – The Fund uses an asset allocation strategy in pursuit of its investment objective. There is a risk that the Fund's allocation among asset classes or investments will cause the Fund's shares to lose value or cause the Fund to underperform other funds with similar investment objectives, or that the investments themselves will not produce the returns expected.

• Investing in Other Funds Risk – The performance of the underlying fund(s) in which the Fund invests could be adversely affected if other entities that invest in the same underlying fund(s) make relatively large investments or redemptions in the underlying fund(s). In addition, because the expenses and costs of the underlying fund(s) are shared by investors in the underlying fund, redemptions by other investors in the underlying fund could result in decreased economies of scale and increased operating expenses for the underlying fund. The Fund, and its shareholders, indirectly bear a portion of the expenses of the underlying fund(s). These transactions might also result in higher brokerage, tax or other costs for the Fund. This risk may be particularly important when one investor owns a substantial portion of any underlying fund. In addition, the Investment Manager has the authority to change the underlying fund(s) in which the Fund invests or to change the percentage of the Fund's investments allocated to each underlying fund. If an underlying fund pays fees to the Investment Manager or its affiliates, such as advisory fees, this could result in the Investment Manager having a potential conflict of interest in selecting the underlying fund(s) in which the Fund invests or in determining the percentage of the Fund's investments allocated to each underlying fund. In addition, the underlying funds are themselves subject to Investment Strategy Risk.

The Fund is subject indirectly to the following risks of the Portfolio Funds:

• Market Risk – Market risk refers to the possibility that the market values of securities that a Portfolio Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Portfolio Fund. Accordingly, an investment in a Portfolio Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Portfolio Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Interest Rate Risk – Debt securities are subject to interest rate risk. In general, if prevailing interest rates rise, the values of debt securities will tend to fall, and if interest rates fall, the values of debt securities will tend to rise. Changes in the value of a debt security usually will not affect the amount of income a Portfolio Fund receives from it but may affect the value of the Portfolio Fund's shares. Interest rate risk is generally greater for debt securities with longer maturities/durations.

• Credit Risk – Credit risk applies to most debt securities, but is generally less of a factor for obligations backed by the "full faith and credit" of the U.S. Government. A Portfolio Fund could lose money if the issuer of a debt security owned by the Fund is unable or perceived to be unable to pay interest or repay principal when it becomes due. Various factors could affect the issuer's actual or perceived willingness or ability to make timely interest or principal payments, including changes in the issuer's financial condition or in general economic conditions. Debt securities backed by an issuer's taxing authority may be subject to legal limits on the issuer's power to increase taxes or otherwise to raise revenue, or may be dependent on legislative appropriation or government aid. Certain debt securities are backed only by revenues derived from a particular project or source, rather than by an issuer's taxing authority, and thus may have a greater risk of default.

• Low and Below Investment Grade Securities Risk – Debt securities with the lowest investment grade rating (e.g., BBB by Standard & Poor's, a division of the McGraw-Hill Companies, Inc. (S&P), or Fitch, Inc. (Fitch) or Baa by Moody's Investors Service, Inc. (Moody's)), or that are below investment grade (which are commonly referred to as "junk bonds") (e.g., BB or below by S&P or Fitch or Ba by Moody's) and unrated securities of comparable quality are more speculative than securities with higher ratings and may experience greater price fluctuations. These securities tend to be more sensitive to credit risk than higher-rated securities, particularly during a downturn in the economy, which is more likely to weaken the ability of the issuers to make principal and interest payments on these securities. These securities typically pay a premium – a higher interest rate or yield – because of the increased risk of loss, including default. These securities also are generally less liquid than higher-rated securities. The securities ratings provided by Moody's, S&P and Fitch are based on analyses by these ratings agencies of the credit quality of the securities and may not take into account every risk related to whether interest or principal will be timely repaid.

• Value Securities Risk – Value securities are securities of companies that may have experienced, for example, adverse business, industry or other developments or may be subject to special risks that have caused the securities to be out of favor and, in turn, potentially undervalued. The market value of a portfolio security may not meet the Investment Manager's future value assessment of that security, or may decline. There is also a risk that it may take longer than expected for the value of these investments to rise to the believed value. In addition, value securities, at times, may not perform as well as growth securities or the stock market in general, and may be out of favor with investors for varying periods of time.

• Growth Securities Risk – Because growth securities typically trade at a higher multiple of earnings than other types of securities, the market values of growth securities may be more sensitive to changes in current or expected earnings than the market values of other types of securities. In addition, growth securities, at times, may not perform as well as value securities or the stock market in general, and may be out of favor with investors for varying periods of time.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Portfolio Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Portfolio Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Index Risk – U.S. Treasury Index Fund's value will generally decline when the performance of its targeted index declines. Because U.S. Treasury Index Fund is designed to track an index before fees and expenses, U.S. Treasury Index Fund cannot purchase other securities that may help offset declines in its index. In addition, because U.S. Treasury Index Fund may not hold all issues included in its index, may not always be fully invested, and bears advisory, administrative and other expenses and transaction costs in trading securities, U.S. Treasury Index Fund's performance may fail to match the performance of its targeted index, after taking expenses into account. It is not possible to invest directly in an index.

• U.S. Government Obligations Risk – While U.S. Treasury obligations are backed by the "full faith and credit" of the U.S. Government, such securities are nonetheless subject to credit risk (i.e., the risk that the U.S. Government may be, or may be perceived to be, unable or unwilling to honor its financial obligations, such as making payments). Securities issued or guaranteed by federal agencies or authorities and U.S. Government-sponsored instrumentalities or enterprises may or may not be backed by the full faith and credit of the U.S. Government. For example, securities issued by the Federal Home Loan Mortgage Corporation, the Federal National Mortgage Association and the Federal Home Loan Banks are neither insured nor guaranteed by the U.S. Government. These securities may be supported by the ability to borrow from the U.S. Treasury or only by the credit of the issuing agency, authority, instrumentality or enterprise and, as a result, are subject to greater credit risk than securities issued or guaranteed by the U.S. Treasury. Securities guaranteed by the Federal Deposit Insurance Corporation under its Temporary Liquidity Guarantee Program (TLGP) are subject to certain risks, including whether such securities will continue to trade in line with recent experience in relation to treasury and government agency securities in terms of yield spread and the volatility of such spread, as well as uncertainty as to how such securities will trade in the secondary market and whether that market will be liquid or illiquid. The TLGP is subject to change. See ABOUT THE FUNDS' INVESTMENTS - U.S. Government and Related Obligations in the Statement of Additional Information for more information.

• Derivatives Risk – Derivatives are financial contracts whose values are, for example, based on (or "derived" from) traditional securities (such as a stock or bond), assets (such as a commodity like gold or a foreign currency), reference rates (such as LIBOR) or market indices (such as the S&P 500® Index). Derivatives involve special risks and may result in losses or may limit a Portfolio Fund's potential gain from favorable market movements. Derivative strategies often involve leverage, which may exaggerate a loss, potentially causing a Portfolio Fund to lose more money than it would have lost had it invested in the underlying security or other asset. The values of derivatives may move in unexpected ways, especially in unusual market conditions, and may result in increased volatility, among other consequences. The use of derivatives may also increase the amount of taxes payable by shareholders holding shares in a taxable account. Other risks arise from a Portfolio Fund's potential inability to terminate or to sell derivative positions. A liquid secondary market may not always exist for the Portfolio Fund's derivative positions at times when the Portfolio Fund might wish to terminate or to sell such positions. Over-the-counter instruments (investments not traded on an exchange) may be illiquid, and transactions in derivatives traded in the over-the-counter market are subject to the risk that the other party will not meet its obligations. The use of derivatives also involves the risks of mispricing or improper valuation and that changes in the value of the derivative may not correlate perfectly with the underlying security, asset, reference rate or index. A Portfolio Fund also may not be able to find a suitable derivative transaction counterparty, and thus may be unable to engage in derivative transactions when it is deemed favorable to do so, or at all. U.S. federal legislation has recently been enacted that provides for new clearing, margin, reporting and registration requirements for participants in the derivatives market. While the ultimate impact is not yet clear, these changes could restrict and/or impose significant costs or other burdens upon the Fund's participation in derivatives transactions. For more information on the risks of derivative investments and strategies, see the Statement of Additional Information.

• Convertible Securities Risk – Certain Portfolio Funds invest in convertible securities, which are subject to the usual risks associated with debt securities, such as interest rate risk and credit risk. Convertible securities also react to changes in the value of the common stock into which they convert. Because the value of a convertible security can be influenced by both interest rates and the common stock's market movements, a convertible security generally is not as sensitive to interest rates as a similar debt security, and generally will not vary in value in response to other factors to the same extent as the underlying common stock. In the event of a liquidation of the issuing company, holders of convertible securities would typically be paid before the company's common stockholders but after holders of any senior debt obligations of the company. A Portfolio Fund may be forced to convert a convertible security before it otherwise would choose to do so, which may decrease the Portfolio Fund's return.

• Non-Diversified Mutual Fund Risk – If a Portfolio Fund is non-diversified, that Portfolio Fund generally may invest a greater percentage of its total assets in the securities of fewer issuers than may a "diversified" fund. This increases the risk that a change in the value of any one investment held by the non-diversified Portfolio Fund could affect the overall value of the Portfolio Fund more than it would affect that of a diversified fund holding a greater number of investments. Accordingly, a non-diversified Portfolio Fund's value will likely be more volatile than the value of more diversified funds. A Portfolio Fund that is non-diversified may not operate as a non-diversified fund at all times.

• Technology Sector Risk – Companies in the technology sector are subject to significant competitive pressures, such as aggressive pricing of their products or services, new market entrants, competition for market share, short product cycles due to an accelerated rate of technological developments and the potential for limited earnings and/or falling profit margins. These companies also face the risks that new services, equipment or technologies will not be accepted by consumers and businesses or will become rapidly obsolete. These factors can affect the profitability of technology companies and, as a result, the value of their securities. Also, patent protection is integral to the success of many companies in the technology sector, and profitability can be affected materially by, among other things, the cost of obtaining (or failing to obtain) patent approvals, the cost of litigating patent infringement and the loss of patent protection for products (which significantly increases pricing pressures and can materially reduce profitability with respect to such products). In addition, many technology companies have limited operating histories. Prices of these companies' securities historically have been more volatile than other securities, especially over the short term. Because certain Portfolio Funds invest a significant portion of their net assets in the equity securities of technology companies, a Portfolio Fund's price may be more volatile than a fund that is invested in a more diverse range of market sectors.

• Health Care Sector Risk - Companies in the health care sector are subject to extensive government regulation. Their profitability can be affected significantly and adversely by restrictions on government reimbursement for medical expenses, government approval of medical products and services, competitive pricing pressures, an increased emphasis on outpatient and other alternative services and other factors. Patent protection is integral to the success of companies in the health care sector, and profitability can be affected materially by, among other things, the cost of obtaining (or failing to obtain) patent approvals, the cost of litigating patent infringement and the loss of patent protection for medical products (which significantly increases pricing pressures and can materially reduce profitability with respect to such products). Companies in the health care sector also potentially are subject to extensive product liability and other similar litigation. Companies in the health care sector are affected by the rising cost of medical products and services, and the effects of such rising costs can be particularly pronounced for companies that are dependent on a relatively limited number of products or services. Medical products also frequently become obsolete due to industry innovation or other causes. Because certain Portfolio Funds invest a significant portion of their net assets in the equity securities of health care companies, a Portfolio Fund's price may be more volatile than a fund that is invested in a more diverse range of market sectors.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class Z shares has varied from year to year.

Year by Year Total Return (%) as of December 31 Each Year

^[18]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    19.33%

Worst:   4th quarter 2008:   -19.26%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns for each period with those of the S&P 500® Index, the Fund's primary benchmark for equity securities, the Barclays U.S. Aggregate Bond Index, the Fund's primary benchmark for debt securities, the Lipper Flexible Portfolio Funds Index and a 50/50 Blended Benchmark. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. The Barclays U.S. Aggregate Bond Index is a market value-weighted index that tracks the daily price, coupon, pay-downs, and total return performance of fixed-rate, publicly placed, dollar-denominated, and non-convertible investment grade debt issues with at least $250 million par amount outstanding and with at least one year to final maturity. The Lipper Flexible Portfolio Funds Index is an equal-weighted index of the 30 largest mutual funds within the Flexible Portfolio fund classification, as defined by Lipper, and shows how the Fund's performance compares with the returns of an index of funds with similar investment objectives. The 50/50 Blended Benchmark was established by the Investment Manager to show how the Fund's performance compares to an equally weighted custom composite of the Fund's primary equity and primary debt benchmarks, the S&P 500® Index and the Barclays U.S. Aggregate Bond Index, respectively. The percentage of the Fund's assets allocated to underlying stock and bond Portfolio Funds will vary, and accordingly the composition of the Fund's portfolio will not always reflect the composition of the 50/50 Blended Benchmark.

Average Annual Total Returns (Columbia Thermostat Fund) (Columbia Thermostat Fund Z)	Inception Date	1 Year	5 Years	Life of Fund
Class Z Shares	Sep. 25, 2002	4.85%	4.21%	7.51%
Class Z Shares returns after taxes on distributions	Sep. 25, 2002	3.80%	3.12%	6.26%
Class Z Shares returns after taxes on distributions and sale of Fund shares	Sep. 25, 2002	3.15%	3.06%	5.97%
S&P 500® Index (reflects no deductions for fees, expenses or taxes)	Sep. 25, 2002	2.11%	(0.25%)	6.85%
Barclays U.S. Aggregate Bond Index (reflects no deductions for fees, expenses or taxes)	Sep. 25, 2002	7.84%	6.50%	5.33%
Lipper Flexible Portfolio Funds Index (reflects no deductions for taxes)	Sep. 25, 2002	(1.16%)	2.02%	7.10%
50-50 S&P 500/Barclays Capital Aggregate Bond (an equally weighted custom composite of the Fund's primary benchmarks for equity and debt securities, established by the Investment Manager; reflects no deductions for fees, expenses or taxes)	Sep. 25, 2002	5.28%	3.54%	6.43%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

(Columbia Acorn European Fund A,C & I) | (Columbia Acorn European Fund)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds. More information about these and other discounts is available from your financial advisor, in the Choosing a Share Class section beginning on page 18 of this prospectus and in Appendix D to the Statement of Additional Information under Sales Charge Waivers beginning on page D-1.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn European Fund A,C & I) (Columbia Acorn European Fund)	Class A Shares		Class C Shares		Class I Shares
Maximum sales charge (load) imposed on purchases, as a % of offering price	5.75%
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[1]	1.00%	[2]

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn European Fund A,C & I) (Columbia Acorn European Fund)		Class A Shares	Class C Shares	Class I Shares
Management fees		1.19%	1.19%	1.19%
Distribution and/or service (Rule 12b-1) fees		0.25%	1.00%	none
Other expenses	[1]	18.29%	19.93%	17.78%
Total annual Fund operating expenses		19.73%	22.12%	18.97%
Fee waivers and/or reimbursements	[2]	(17.98%)	(19.62%)	(17.66%)
Total annual Fund operating expenses after fee waivers and/or reimbursements		1.75%	2.50%	1.31%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class A, Class C or Class I shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire on April 30, 2013, they are only reflected in the 1 year example and the first year of the 3 year example.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn European Fund) (Columbia Acorn European Fund A,C & I) (USD $)	1 Year	3 Years
Class A Shares	743	4,038
Class C Shares	353	4,045
Class I Shares	133	3,537

Expense Example, No Redemption (Columbia Acorn European Fund) (USD $)	1 Year	3 Years
Class C Shares (Columbia Acorn European Fund A,C & I)	253	4,045

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 17% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 80% of its net assets (plus any borrowing for investment purposes) in European companies. Under normal circumstances, the Fund invests at least 70% of its total assets in companies in Western European countries (for example, the United Kingdom, Germany, France and Italy), but also may invest up to 30% of its total assets in companies in emerging Central and Eastern European countries (for example, Poland, the Czech Republic, Turkey and Cyprus), including up to 10% of its total assets in companies in Russia and the Ukraine. For purposes of the Fund's policies, the Fund may invest in a company if (i) it is domiciled in, or the principal trading market for its securities is in, a European country, (ii) it derives 50% or more of its economic value from goods produced, sales made or services performed or has at least 50% of its assets in a European country or (iii) it is a holding company that predominantly holds shares in such companies. The Fund may invest in a variety of countries, industries and sectors and does not attempt to invest a specific percentage of its assets in any given country, industry or sector.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to initially invest in a limited number of companies (generally under 100), offering the potential to provide above-average growth over time.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Currency Risk – Securities denominated in non-U.S. dollar currencies are subject to the risk that, for example, if the value of a foreign currency were to decline against the U.S. dollar, such decline would reduce the U.S. dollar value of any securities held by the Fund denominated in that currency.

• Special Situations Risk – Securities of companies that are involved in an initial public offering or a major corporate event, such as a business consolidation or restructuring, which may present special risk because of the high degree of uncertainty that can be associated with such events. Securities issued in initial public offerings often are issued by companies that are in the early stages of development, have a history of little or no revenues and may operate at a loss following the offering. It is possible that there will be no active trading market for the securities after the offering, and that the market price of the securities may be subject to significant and unpredictable fluctuations. Investing in special situations may have a magnified effect on the performance of funds with small amounts of assets.

Performance Information

Because the Fund commenced investment operations on August 19, 2011, no year-by-year total return bar chart or average annual total return table is being presented. The year-by year-total return bar chart and the average annual total return table will be provided after the Fund has annual returns for at least one calendar year.

Recent performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

(Columbia Acorn European Fund Z) | (Columbia Acorn European Fund)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn European Fund)	Class Z Shares (Columbia Acorn European Fund Z)
Maximum sales charge (load) imposed on purchases, as a % of offering price	none
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn European Fund)		Class Z Shares (Columbia Acorn European Fund Z)
Management fees		1.19%
Distribution and/or service (Rule 12b-1) fees		none
Other expenses	[1]	17.83%
Total annual Fund operating expenses		19.02%
Fee waivers and/or reimbursements	[2]	(17.52%)
Total annual Fund operating expenses after fee waivers and/or reimbursements		1.50%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class Z shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire on April 30, 2013, they are only reflected in the 1 year example and the first year of the 3 year example.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn European Fund) (USD $)	1 Year	3 Years
Class Z Shares (Columbia Acorn European Fund Z)	153	3,557

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 17% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 80% of its net assets (plus any borrowing for investment purposes) in European companies. Under normal circumstances, the Fund invests at least 70% of its total assets in companies in Western European countries (for example, the United Kingdom, Germany, France and Italy), but also may invest up to 30% of its total assets in companies in emerging Central and Eastern European countries (for example, Poland, the Czech Republic, Turkey and Cyprus), including up to 10% of its total assets in companies in Russia and the Ukraine. For purposes of the Fund's policies, the Fund may invest in a company if (i) it is domiciled in, or the principal trading market for its securities is in, a European country, (ii) it derives 50% or more of its economic value from goods produced, sales made or services performed or has at least 50% of its assets in a European country or (iii) it is a holding company that predominantly holds shares in such companies. The Fund may invest in a variety of countries, industries and sectors and does not attempt to invest a specific percentage of its assets in any given country, industry or sector.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to initially invest in a limited number of companies (generally under 100), offering the potential to provide above-average growth over time.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Currency Risk – Securities denominated in non-U.S. dollar currencies are subject to the risk that, for example, if the value of a foreign currency were to decline against the U.S. dollar, such decline would reduce the U.S. dollar value of any securities held by the Fund denominated in that currency.

• Special Situations Risk – Securities of companies that are involved in an initial public offering or a major corporate event, such as a business consolidation or restructuring, which may present special risk because of the high degree of uncertainty that can be associated with such events. Securities issued in initial public offerings often are issued by companies that are in the early stages of development, have a history of little or no revenues and may operate at a loss following the offering. It is possible that there will be no active trading market for the securities after the offering, and that the market price of the securities may be subject to significant and unpredictable fluctuations. Investing in special situations may have a magnified effect on the performance of funds with small amounts of assets.

Performance Information

Because the Fund commenced investment operations on August 19, 2011, no year-by-year total return bar chart or average annual total return table is being presented. The year-by year-total return bar chart and the average annual total return table will be provided after the Fund has annual returns for at least one calendar year.

Recent performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

(Columbia Acorn Emerging Markets Fund A,C & I) | (Columbia Acorn Emerging Markets Fund)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds. More information about these and other discounts is available from your financial advisor, in the Choosing a Share Class section beginning on page 18 of this prospectus and in Appendix D to the Statement of Additional Information under Sales Charge Waivers beginning on page D-1.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn Emerging Markets Fund A,C & I) (Columbia Acorn Emerging Markets Fund)	Class A Shares		Class C Shares		Class I Shares
Maximum sales charge (load) imposed on purchases, as a % of offering price	5.75%
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[1]	1.00%	[2]

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn Emerging Markets Fund A,C & I) (Columbia Acorn Emerging Markets Fund)		Class A Shares	Class C Shares	Class I Shares
Management fees		1.25%	1.25%	1.25%
Distribution and/or service (Rule 12b-1) fees		0.25%	1.00%	none
Other expenses	[1]	12.72%	13.09%	12.05%
Total annual Fund operating expenses	[2]	14.22%	15.34%	13.30%
Fee waivers and/or reimbursements	[3]	(12.37%)	(12.74%)	(11.89%)
Total annual Fund operating expenses after fee waivers and/or reimbursements		1.85%	2.60%	1.41%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class A, Class C or Class I shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire on April 30, 2013, they are only reflected in the 1 year example and the first year of the 3 year example.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn Emerging Markets Fund) (Columbia Acorn Emerging Markets Fund A,C & I) (USD $)	1 Year	3 Years
Class A Shares	752	3,268
Class C Shares	363	3,088
Class I Shares	144	2,675

Expense Example, No Redemption (Columbia Acorn Emerging Markets Fund) (USD $)	1 Year	3 Years
Class C Shares (Columbia Acorn Emerging Markets Fund A,C & I)	263	3,088

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 9% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 80% of its net assets (plus any borrowing for investment purposes) in companies located in emerging market countries, including frontier market countries. Emerging market countries are those countries whose economies are developing or emerging from underdevelopment (for example, China, India, Poland and Turkey). Frontier market countries generally have smaller economies and even less developed capital markets than traditional emerging market countries (for example, Vietnam, Colombia, Nigeria and Kazakhstan). For purposes of the Fund's policies, the Fund may invest in a company if (i) it is domiciled in, or the principal trading market for its securities is in, an emerging market country, (ii) it derives 50% or more of its economic value from goods produced, sales made or services performed or has at least 50% of its assets in an emerging market country or countries or (iii) it is a holding company that predominantly holds shares in such companies. The Fund may invest in a variety of countries, industries and sectors and does not attempt to invest a specific percentage of its assets in any given country, industry or sector.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion. Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to initially invest in a limited number of companies (generally under 100), offering the potential to provide above-average growth over time.

Generally, the Investment Manager will determine which countries are emerging market countries by reference to the countries included in the S&P Emerging Markets Broad Market Index (BMI), and will determine which countries are frontier market countries by reference to the countries included in the S&P Frontier BMI. In addition, the Fund may invest in certain developing market countries that are not included in either the S&P Emerging Markets BMI or the S&P Frontier BMI (for example, Serbia and Senegal), but which are included on another independent third-party listing of emerging market and/or frontier market countries. The Investment Manager will make all determinations as to whether a company is an emerging market company at the time of investment. The countries that comprise emerging market countries, including frontier market countries, may change from time to time.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Frontier Market Risk — Frontier market countries generally have smaller economies and even less developed capital markets than traditional emerging market countries and, as a result, the risks of investing in emerging market countries are magnified in frontier market countries. The magnification of risks are the result of: potential for extreme price volatility and illiquidity in frontier market countries; government ownership or control of parts of private sector and of certain companies; trade barriers, exchange controls, managed adjustments in relative currency values and other protectionist measures imposed or negotiated by the countries with which frontier market countries trade; and the relatively new and unsettled securities laws in many frontier market countries.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Currency Risk – Securities denominated in non-U.S. dollar currencies are subject to the risk that, for example, if the value of a foreign currency were to decline against the U.S. dollar, such decline would reduce the U.S. dollar value of any securities held by the Fund denominated in that currency.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Special Situations Risk – Securities of companies that are involved in an initial public offering or a major corporate event, such as a business consolidation or restructuring, which may present special risk because of the high degree of uncertainty that can be associated with such events. Securities issued in initial public offerings often are issued by companies that are in the early stages of development, have a history of little or no revenues and may operate at a loss following the offering. It is possible that there will be no active trading market for the securities after the offering, and that the market price of the securities may be subject to significant and unpredictable fluctuations. Investing in special situations may have a magnified effect on the performance of funds with small amounts of assets.

Performance Information

Because the Fund commenced investment operations on August 19, 2011, no year-by-year total return bar chart or average annual total return table is being presented. The year-by year-total return bar chart and the average annual total return table will be provided after the Fund has annual returns for at least one calendar year.

Recent performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

(Columbia Acorn Emerging Markets Fund Z) | (Columbia Acorn Emerging Markets Fund)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn Emerging Markets Fund)	Class Z Shares (Columbia Acorn Emerging Markets Fund Z)
Maximum sales charge (load) imposed on purchases, as a % of offering price	none
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn Emerging Markets Fund)		Class Z Shares (Columbia Acorn Emerging Markets Fund Z)
Management fees		1.25%
Distribution and/or service (Rule 12b-1) fees		none
Other expenses	[1]	12.10%
Total annual Fund operating expenses	[2]	13.35%
Fee waivers and/or reimbursements	[3]	(11.75%)
Total annual Fund operating expenses after fee waivers and/or reimbursements		1.60%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class Z shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire on April 30, 2013, they are only reflected in the 1 year example and the first year of the 3 year example.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn Emerging Markets Fund) (USD $)	1 Year	3 Years
Class Z Shares (Columbia Acorn Emerging Markets Fund Z)	163	2,698

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 9% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 80% of its net assets (plus any borrowing for investment purposes) in companies located in emerging market countries, including frontier market countries. Emerging market countries are those countries whose economies are developing or emerging from underdevelopment (for example, China, India, Poland and Turkey). Frontier market countries generally have smaller economies and even less developed capital markets than traditional emerging market countries (for example, Vietnam, Colombia, Nigeria and Kazakhstan). For purposes of the Fund's policies, the Fund may invest in a company if (i) it is domiciled in, or the principal trading market for its securities is in, an emerging market country, (ii) it derives 50% or more of its economic value from goods produced, sales made or services performed or has at least 50% of its assets in an emerging market country or countries or (iii) it is a holding company that predominantly holds shares in such companies. The Fund may invest in a variety of countries, industries and sectors and does not attempt to invest a specific percentage of its assets in any given country, industry or sector.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion. Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to initially invest in a limited number of companies (generally under 100), offering the potential to provide above-average growth over time.

Generally, the Investment Manager will determine which countries are emerging market countries by reference to the countries included in the S&P Emerging Markets Broad Market Index (BMI), and will determine which countries are frontier market countries by reference to the countries included in the S&P Frontier BMI. In addition, the Fund may invest in certain developing market countries that are not included in either the S&P Emerging Markets BMI or the S&P Frontier BMI (for example, Serbia and Senegal), but which are included on another independent third-party listing of emerging market and/or frontier market countries. The Investment Manager will make all determinations as to whether a company is an emerging market company at the time of investment. The countries that comprise emerging market countries, including frontier market countries, may change from time to time.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Frontier Market Risk — Frontier market countries generally have smaller economies and even less developed capital markets than traditional emerging market countries and, as a result, the risks of investing in emerging market countries are magnified in frontier market countries. The magnification of risks are the result of: potential for extreme price volatility and illiquidity in frontier market countries; government ownership or control of parts of private sector and of certain companies; trade barriers, exchange controls, managed adjustments in relative currency values and other protectionist measures imposed or negotiated by the countries with which frontier market countries trade; and the relatively new and unsettled securities laws in many frontier market countries.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Currency Risk – Securities denominated in non-U.S. dollar currencies are subject to the risk that, for example, if the value of a foreign currency were to decline against the U.S. dollar, such decline would reduce the U.S. dollar value of any securities held by the Fund denominated in that currency.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Special Situations Risk – Securities of companies that are involved in an initial public offering or a major corporate event, such as a business consolidation or restructuring, which may present special risk because of the high degree of uncertainty that can be associated with such events. Securities issued in initial public offerings often are issued by companies that are in the early stages of development, have a history of little or no revenues and may operate at a loss following the offering. It is possible that there will be no active trading market for the securities after the offering, and that the market price of the securities may be subject to significant and unpredictable fluctuations. Investing in special situations may have a magnified effect on the performance of funds with small amounts of assets.

Performance Information

Because the Fund commenced investment operations on August 19, 2011, no year-by-year total return bar chart or average annual total return table is being presented. The year-by year-total return bar chart and the average annual total return table will be provided after the Fund has annual returns for at least one calendar year.

Recent performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

[1] Contingent deferred sales charges (CDSC) on certain investments of between $1 million and $50 million redeemed within 18 months of purchase, charged as follows: 1.00% CDSC if redeemed within 12 months of purchase, and 0.50% CDSC if redeemed more than 12, but less than 18, months of purchase, with certain limited exceptions.

[2] This charge applies to investors who buy Class C shares and redeem them within one year of purchase, with certain limited exceptions.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] This charge decreases over time. See About Class B Shares - Sales Charges and Commissions for details.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] Contingent deferred sales charges (CDSC) on certain investments of between $1 million and $50 million redeemed within 18 months of purchase, charged as follows: 1.00% CDSC if redeemed within 12 months of purchase, and 0.50% CDSC if redeemed more than 12, but less than 18, months of purchase, with certain limited exceptions.

[2] This charge applies to investors who buy Class C shares and redeem them within one year of purchase, with certain limited exceptions.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[2] Columbia Management Investment Services Corp., the Fund's transfer agent, has contractually agreed, through August 14, 2013, to waive a portion of total annual Fund operating expenses attributable to transfer agency fees incurred by Class A shares and Class C shares. Pursuant to this agreement, total annual Fund operating expenses will be reduced by 0.04% for Class A shares and 0.02% for Class C shares.

[1] This charge decreases over time. See About Class B Shares - Sales Charges and Commissions for details.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[2] Columbia Management Investment Services Corp., the Fund's transfer agent, has contractually agreed, through August 14, 2013, to waive a portion of total annual Fund operating expenses attributable to transfer agency fees incurred by Class B shares. Pursuant to this agreement, total annual Fund operating expenses will be reduced by 0.03% for Class B shares.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] Contingent deferred sales charges (CDSC) on certain investments of between $1 million and $50 million redeemed within 18 months of purchase, charged as follows: 1.00% CDSC if redeemed within 12 months of purchase, and 0.50% CDSC if redeemed more than 12, but less than 18, months of purchase, with certain limited exceptions.

[2] This charge applies to investors who buy Class C shares and redeem them within one year of purchase, with certain limited exceptions.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] This charge decreases over time. See About Class B Shares - Sales Charges and Commissions for details.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] Contingent deferred sales charges (CDSC) on certain investments of between $1 million and $50 million redeemed within 18 months of purchase, charged as follows: 1.00% CDSC if redeemed within 12 months of purchase, and 0.50% CDSC if redeemed more than 12, but less than 18, months of purchase, with certain limited exceptions.

[2] This charge applies to investors who buy Class C shares and redeem them within one year of purchase, with certain limited exceptions.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] This charge decreases over time. See About Class B Shares - Sales Charges and Commissions for details.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] Contingent deferred sales charges (CDSC) on certain investments of between $1 million and $50 million redeemed within 18 months of purchase, charged as follows: 1.00% CDSC if redeemed within 12 months of purchase, and 0.50% CDSC if redeemed more than 12, but less than 18, months of purchase, with certain limited exceptions.

[2] This charge applies to investors who buy Class C shares and redeem them within one year of purchase, with certain limited exceptions.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] This charge decreases over time. See About Class B Shares - Sales Charges and Commissions for details.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] Contingent deferred sales charges (CDSC) on certain investments of between $1 million and $50 million redeemed within 18 months of purchase, charged as follows: 1.00% CDSC if redeemed within 12 months of purchase, and 0.50% CDSC if redeemed more than 12, but less than 18, months of purchase, with certain limited exceptions.

[2] This charge applies to investors who buy Class C shares and redeem them within one year of purchase, with certain limited exceptions.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[2] Total annual Fund operating expenses include the annualized average weighted fees and expenses of acquired funds (underlying Portfolio Funds). As a result, the amount shown is higher than the ratio of expenses to average net assets included in Financial Highlights, which reflects only those expenses paid directly by the Fund.

[3] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that ordinary operating expenses (excluding distribution and service fees, interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies) do not exceed the annual rate of 0.25% of the Fund's average daily net assets, through April 30, 2013. The figure shown here is the amount of expected waivers and/or reimbursements. This fee and expense arrangement may only be modified or amended with approval from all parties to such arrangement, including the Fund and the Investment Manager.

[1] This charge decreases over time. See About Class B Shares - Sales Charges and Commissions for details.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[2] Total annual Fund operating expenses include the annualized average weighted fees and expenses of acquired funds (underlying Portfolio Funds). As a result, the amount shown is higher than the ratio of expenses to average net assets included in Financial Highlights, which reflects only those expenses paid directly by the Fund.

[3] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that ordinary operating expenses (excluding distribution and service fees, interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies) do not exceed the annual rate of 0.25% of the Fund's average daily net assets, through April 30, 2013. The figure shown here is the amount of expected waivers and/or reimbursements. This fee and expense arrangement may only be modified or amended with approval from all parties to such arrangement, including the Fund and the Investment Manager.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[2] Total annual Fund operating expenses include the annualized average weighted fees and expenses of acquired funds (underlying Portfolio Funds). As a result, the amount shown is higher than the ratio of expenses to average net assets included in Financial Highlights, which reflects only those expenses paid directly by the Fund.

[3] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that ordinary operating expenses (excluding distribution and service fees, interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies) do not exceed the annual rate of 0.25% of the Fund's average daily net assets, through April 30, 2013. The figure shown here is the amount of expected waivers and/or reimbursements. This fee and expense arrangement may only be modified or amended with approval from all parties to such arrangement, including the Fund and the Investment Manager.

[1] Contingent deferred sales charges (CDSC) on certain investments of between $1 million and $50 million redeemed within 18 months of purchase, charged as follows: 1.00% CDSC if redeemed within 12 months of purchase, and 0.50% CDSC if redeemed more than 12, but less than 18, months of purchase, with certain limited exceptions.

[2] This charge applies to investors who buy Class C shares and redeem them within one year of purchase, with certain limited exceptions.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[2] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that the ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) do not exceed the annual rates of 1.75%, 2.50% and 1.31% of the Fund's average daily net assets attributable to Class A, Class C and Class I shares, respectively, through April 30, 2013. The Investment Manager may recoup any fees waived and/or expenses reimbursed with respect to any share class of the Fund for a one-year period following the date of such fee waiver and/or reimbursement if such recovery does not cause the Fund's ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) to exceed the annual rates set forth in this prospectus, or to exceed such annual rate as may be in place at the time of the recoupment, whichever is less. This expense arrangement may only be modified or amended with approval from all parties to such arrangements, including the Fund and the Investment Manager.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[2] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that the ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) do not exceed the annual rate of 1.50% of the Fund's average daily net assets attributable to Class Z shares, through April 30, 2013. The Investment Manager may recoup any fees waived and/or expenses reimbursed with respect to any share class of the Fund for a one-year period following the date of such fee waiver and/or reimbursement if such recovery does not cause the Fund's ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) to exceed the annual rates set forth in this prospectus, or to exceed such annual rate as may be in place at the time of the recoupment, whichever is less. This expense arrangement may only be modified or amended with approval from all parties to such arrangements, including the Fund and the Investment Manager.

[1] Contingent deferred sales charges (CDSC) on certain investments of between $1 million and $50 million redeemed within 18 months of purchase, charged as follows: 1.00% CDSC if redeemed within 12 months of purchase, and 0.50% CDSC if redeemed more than 12, but less than 18, months of purchase, with certain limited exceptions.

[2] This charge applies to investors who buy Class C shares and redeem them within one year of purchase, with certain limited exceptions.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[2] During its initial fiscal period, the Fund had acquired fund fees and expenses of 0.04% on an annualized basis. Based on assumptions as to the Fund's expected investments in other investment companies during the current fiscal year, acquired fund fees and expenses are expected to be less than 0.01%.

[3] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that the ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) do not exceed the annual rates of 1.85%, 2.60% and 1.41% of the Fund's average daily net assets attributable to Class A, Class C and Class I shares, respectively, through April 30, 2013. The Investment Manager may recoup any fees waived and/or expenses reimbursed with respect to any share class of the Fund for a one-year period following the date of such fee waiver and/or reimbursement if such recovery does not cause the Fund's ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) to exceed the annual rates set forth in this prospectus, or to exceed such annual rate as may be in place at the time of the recoupment, whichever is less. This expense arrangement may only be modified or amended with approval from all parties to such arrangements, including the Fund and the Investment Manager.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[2] During its initial fiscal period, the Fund had acquired fund fees and expenses of 0.04% on an annualized basis. Based on assumptions as to the Fund's expected investments in other investment companies during the current fiscal year, acquired fund fees and expenses are expected to be less than 0.01%.

[3] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that the ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) do not exceed the annual rate of 1.60% of the Fund's average daily net assets attributable to Class Z shares, through April 30, 2013. The Investment Manager may recoup any fees waived and/or expenses reimbursed with respect to any share class of the Fund for a one-year period following the date of such fee waiver and/or reimbursement if such recovery does not cause the Fund's ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) to exceed the annual rates set forth in this prospectus, or to exceed such annual rate as may be in place at the time of the recoupment, whichever is less. This expense arrangement may only be modified or amended with approval from all parties to such arrangements, including the Fund and the Investment Manager.

[1] Year-to-date return as of March 31, 2012: 15.43%

[2] Year-to-date return as of March 31, 2012: 15.25%

[3] Year-to-date return as of March 31, 2012: 15.49%

[4] Year-to-date return as of March 31, 2012: 14.99%

[5] Year-to-date return as of March 31, 2012: 14.77%

[6] Year-to-date return as of March 31, 2012: 15.07%

[7] Year-to-date return as of March 31, 2012: 16.27%

[8] Year-to-date return as of March 31, 2012: 16.06%

[9] Year-to-date return as of March 31, 2012: 16.38%

[10] Year-to-date return as of March 31, 2012: 17.65%

[11] Year-to-date return as of March 31, 2012: 17.48%

[12] Year-to-date return as of March 31, 2012: 17.70%

[13] Year-to-date return as of March 31, 2012: 11.29%

[14] Year-to-date return as of March 31, 2012: 11.13%

[15] Year-to-date return as of March 31, 2012: 11.37%

[16] Year-to-date return as of March 31, 2012: 8.19%

[17] Year-to-date return as of March 31, 2012: 8.06%

[18] Year-to-date return as of March 31, 2012: 8.29%

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Average Annual Total Returns	0 Months Ended
	May 01, 2012
(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund) | Russell 2500 Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	(2.51%)
5 Years	1.24%
10 Years	6.57%
(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund) | S&P 500® Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	2.11%
5 Years	(0.25%)
10 Years	2.92%
(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund) | Russell 2000 Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	(4.18%)
5 Years	0.15%
10 Years	5.62%
(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund) | Class A Shares
Average Annual Return:
1 Year	(10.36%)
5 Years	0.62%
10 Years	7.21%
(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund) | Class A Shares | returns after taxes on distributions
Average Annual Return:
1 Year	(10.94%)
5 Years	0.10%
10 Years	6.65%
(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund) | Class A Shares | returns after taxes on distributions and sale of Fund shares
Average Annual Return:
1 Year	(5.94%)
5 Years	0.53%
10 Years	6.32%
(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund) | Class C Shares
Average Annual Return:
1 Year	(6.53%)
5 Years	1.02%
10 Years	7.04%
(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund) | Class I Shares
Average Annual Return:
1 Year	(4.57%)
5 Years	2.14%
10 Years	8.25%
(Columbia Acorn Fund B) | (Columbia Acorn Fund) | Russell 2500 Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	(2.51%)
5 Years	1.24%
10 Years	6.57%
(Columbia Acorn Fund B) | (Columbia Acorn Fund) | S&P 500® Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	2.11%
5 Years	(0.25%)
10 Years	2.92%
(Columbia Acorn Fund B) | (Columbia Acorn Fund) | Russell 2000 Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	(4.18%)
5 Years	0.15%
10 Years	5.62%
(Columbia Acorn Fund B) | (Columbia Acorn Fund) | Class B Shares
Average Annual Return:
1 Year	(9.86%)
5 Years	0.89%
10 Years	7.17%
(Columbia Acorn Fund B) | (Columbia Acorn Fund) | Class B Shares | returns after taxes on distributions
Average Annual Return:
1 Year	(10.50%)
5 Years	0.33%
10 Years	6.59%
(Columbia Acorn Fund B) | (Columbia Acorn Fund) | Class B Shares | returns after taxes on distributions and sale of Fund shares
Average Annual Return:
1 Year	(5.51%)
5 Years	0.76%
10 Years	6.29%
(Columbia Acorn Fund Z) | (Columbia Acorn Fund) | Russell 2500 Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	(2.51%)
5 Years	1.24%
10 Years	6.57%
(Columbia Acorn Fund Z) | (Columbia Acorn Fund) | S&P 500® Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	2.11%
5 Years	(0.25%)
10 Years	2.92%
(Columbia Acorn Fund Z) | (Columbia Acorn Fund) | Russell 2000 Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	(4.18%)
5 Years	0.15%
10 Years	5.62%
(Columbia Acorn Fund Z) | (Columbia Acorn Fund) | Class Z Shares
Average Annual Return:
1 Year	(4.61%)
5 Years	2.12%
10 Years	8.24%
(Columbia Acorn Fund Z) | (Columbia Acorn Fund) | Class Z Shares | returns after taxes on distributions
Average Annual Return:
1 Year	(5.23%)
5 Years	1.58%
10 Years	7.66%
(Columbia Acorn Fund Z) | (Columbia Acorn Fund) | Class Z Shares | returns after taxes on distributions and sale of Fund shares
Average Annual Return:
1 Year	(2.13%)
5 Years	1.81%
10 Years	7.25%
(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | S&P Global Ex-U.S. Between $500 Million and $5 Billion® Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	(16.94%)
5 Years	(0.58%)
10 Years	11.10%
(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | S&P Global Ex-U.S. SmallCap® Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	(17.40%)
5 Years	(2.14%)
10 Years	10.33%
(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)
Average Annual Return:
1 Year	(12.14%)
5 Years	(4.72%)
10 Years	4.67%
(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | Class A Shares
Average Annual Return:
1 Year	(19.29%)
5 Years	(1.33%)
10 Years	9.20%
(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | Class A Shares | returns after taxes on distributions
Average Annual Return:
1 Year	(19.82%)
5 Years	(1.79%)
10 Years	8.73%
(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | Class A Shares | returns after taxes on distributions and sale of Fund shares
Average Annual Return:
1 Year	(12.29%)
5 Years	(1.09%)
10 Years	8.23%
(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | Class C Shares
Average Annual Return:
1 Year	(15.85%)
5 Years	(0.93%)
10 Years	9.03%
(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | Class I Shares
Average Annual Return:
1 Year	(14.02%)
5 Years	0.22%
10 Years	10.28%
(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | Class R Shares
Average Annual Return:
1 Year	(14.60%)
5 Years	(0.42%)
10 Years	9.58%
(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | Class R5 Shares
Average Annual Return:
1 Year	(14.07%)
5 Years	0.19%
10 Years	10.26%
(Columbia Acorn International B) | (Columbia Acorn International) | S&P Global Ex-U.S. Between $500 Million and $5 Billion® Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	(16.94%)
5 Years	(0.58%)
10 Years	11.10%
(Columbia Acorn International B) | (Columbia Acorn International) | S&P Global Ex-U.S. SmallCap® Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	(17.40%)
5 Years	(2.14%)
10 Years	10.33%
(Columbia Acorn International B) | (Columbia Acorn International) | MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)
Average Annual Return:
1 Year	(12.14%)
5 Years	(4.72%)
10 Years	4.67%
(Columbia Acorn International B) | (Columbia Acorn International) | Class B Shares
Average Annual Return:
1 Year	(19.07%)
5 Years	(1.13%)
10 Years	9.12%
(Columbia Acorn International B) | (Columbia Acorn International) | Class B Shares | returns after taxes on distributions
Average Annual Return:
1 Year	(19.63%)
5 Years	(1.53%)
10 Years	8.74%
(Columbia Acorn International B) | (Columbia Acorn International) | Class B Shares | returns after taxes on distributions and sale of Fund shares
Average Annual Return:
1 Year	(12.13%)
5 Years	(0.90%)
10 Years	8.20%
(Columbia Acorn International Z) | (Columbia Acorn International) | S&P Global Ex-U.S. Between $500 Million and $5 Billion® Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	(16.94%)
5 Years	(0.58%)
10 Years	11.10%
(Columbia Acorn International Z) | (Columbia Acorn International) | S&P Global Ex-U.S. SmallCap® Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	(17.40%)
5 Years	(2.14%)
10 Years	10.33%
(Columbia Acorn International Z) | (Columbia Acorn International) | MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)
Average Annual Return:
1 Year	(12.14%)
5 Years	(4.72%)
10 Years	4.67%
(Columbia Acorn International Z) | (Columbia Acorn International) | Class Z Shares
Average Annual Return:
1 Year	(14.06%)
5 Years	0.20%
10 Years	10.27%
(Columbia Acorn International Z) | (Columbia Acorn International) | Class Z Shares | returns after taxes on distributions
Average Annual Return:
1 Year	(14.63%)
5 Years	(0.32%)
10 Years	9.71%
(Columbia Acorn International Z) | (Columbia Acorn International) | Class Z Shares | returns after taxes on distributions and sale of Fund shares
Average Annual Return:
1 Year	(8.88%)
5 Years	0.20%
10 Years	9.18%
(Columbia Acorn USA A,C & I) | (Columbia Acorn USA) | Russell 2000 Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	(4.18%)
5 Years	0.15%
10 Years	5.62%
(Columbia Acorn USA A,C & I) | (Columbia Acorn USA) | Class A Shares
Average Annual Return:
1 Year	(10.66%)
5 Years	(0.65%)
10 Years	5.30%
(Columbia Acorn USA A,C & I) | (Columbia Acorn USA) | Class A Shares | returns after taxes on distributions
Average Annual Return:
1 Year	(10.74%)
5 Years	(0.95%)
10 Years	5.02%
(Columbia Acorn USA A,C & I) | (Columbia Acorn USA) | Class A Shares | returns after taxes on distributions and sale of Fund shares
Average Annual Return:
1 Year	(6.81%)
5 Years	(0.55%)
10 Years	4.63%
(Columbia Acorn USA A,C & I) | (Columbia Acorn USA) | Class C Shares
Average Annual Return:
1 Year	(6.86%)
5 Years	(0.25%)
10 Years	5.14%
(Columbia Acorn USA A,C & I) | (Columbia Acorn USA) | Class I Shares
Average Annual Return:
1 Year	(4.88%)
5 Years	0.83%
10 Years	6.31%
(Columbia Acorn USA B) | (Columbia Acorn USA) | Russell 2000 Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	(4.18%)
5 Years	0.15%
10 Years	5.62%
(Columbia Acorn USA B) | (Columbia Acorn USA) | Class B Shares
Average Annual Return:
1 Year	(10.36%)
5 Years	(0.45%)
10 Years	5.25%
(Columbia Acorn USA B) | (Columbia Acorn USA) | Class B Shares | returns after taxes on distributions
Average Annual Return:
1 Year	(10.46%)
5 Years	(0.77%)
10 Years	4.95%
(Columbia Acorn USA B) | (Columbia Acorn USA) | Class B Shares | returns after taxes on distributions and sale of Fund shares
Average Annual Return:
1 Year	(6.60%)
5 Years	(0.37%)
10 Years	4.59%
(Columbia Acorn USA Z) | (Columbia Acorn USA) | Russell 2000 Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	(4.18%)
5 Years	0.15%
10 Years	5.62%
(Columbia Acorn USA Z) | (Columbia Acorn USA) | Class Z Shares
Average Annual Return:
1 Year	(4.95%)
5 Years	0.82%
10 Years	6.30%
(Columbia Acorn USA Z) | (Columbia Acorn USA) | Class Z Shares | returns after taxes on distributions
Average Annual Return:
1 Year	(5.04%)
5 Years	0.52%
10 Years	6.02%
(Columbia Acorn USA Z) | (Columbia Acorn USA) | Class Z Shares | returns after taxes on distributions and sale of Fund shares
Average Annual Return:
1 Year	(3.10%)
5 Years	0.69%
10 Years	5.54%
(Columbia Acorn Select A,C & I) | (Columbia Acorn Select) | S&P 500® Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	2.11%
5 Years	(0.25%)
10 Years	2.92%
(Columbia Acorn Select A,C & I) | (Columbia Acorn Select) | S&P MidCap 400® Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	(1.73%)
5 Years	3.32%
10 Years	7.04%
(Columbia Acorn Select A,C & I) | (Columbia Acorn Select) | Class A Shares
Average Annual Return:
1 Year	(21.43%)
5 Years	(2.52%)
10 Years	5.07%
(Columbia Acorn Select A,C & I) | (Columbia Acorn Select) | Class A Shares | returns after taxes on distributions
Average Annual Return:
1 Year	(21.83%)
5 Years	(2.76%)
10 Years	4.82%
(Columbia Acorn Select A,C & I) | (Columbia Acorn Select) | Class A Shares | returns after taxes on distributions and sale of Fund shares
Average Annual Return:
1 Year	(13.89%)
5 Years	(2.16%)
10 Years	4.40%
(Columbia Acorn Select A,C & I) | (Columbia Acorn Select) | Class C Shares
Average Annual Return:
1 Year	(18.09%)
5 Years	(2.15%)
10 Years	4.89%
(Columbia Acorn Select A,C & I) | (Columbia Acorn Select) | Class I Shares
Average Annual Return:
1 Year	(16.25%)
5 Years	(1.03%)
10 Years	6.07%
(Columbia Acorn Select B) | (Columbia Acorn Select) | S&P 500® Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	2.11%
5 Years	(0.25%)
10 Years	2.92%
(Columbia Acorn Select B) | (Columbia Acorn Select) | S&P MidCap 400® Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	(1.73%)
5 Years	3.32%
10 Years	7.04%
(Columbia Acorn Select B) | (Columbia Acorn Select) | Class B Shares
Average Annual Return:
1 Year	(21.22%)
5 Years	(2.36%)
10 Years	5.00%
(Columbia Acorn Select B) | (Columbia Acorn Select) | Class B Shares | returns after taxes on distributions
Average Annual Return:
1 Year	(21.49%)
5 Years	(2.58%)
10 Years	4.77%
(Columbia Acorn Select B) | (Columbia Acorn Select) | Class B Shares | returns after taxes on distributions and sale of Fund shares
Average Annual Return:
1 Year	(13.77%)
5 Years	(2.00%)
10 Years	4.36%
(Columbia Acorn Select Z) | (Columbia Acorn Select) | S&P 500® Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	2.11%
5 Years	(0.25%)
10 Years	2.92%
(Columbia Acorn Select Z) | (Columbia Acorn Select) | S&P MidCap 400® Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	(1.73%)
5 Years	3.32%
10 Years	7.04%
(Columbia Acorn Select Z) | (Columbia Acorn Select) | Class Z Shares
Average Annual Return:
1 Year	(16.37%)
5 Years	(1.07%)
10 Years	6.05%
(Columbia Acorn Select Z) | (Columbia Acorn Select) | Class Z Shares | returns after taxes on distributions
Average Annual Return:
1 Year	(16.87%)
5 Years	(1.33%)
10 Years	5.77%
(Columbia Acorn Select Z) | (Columbia Acorn Select) | Class Z Shares | returns after taxes on distributions and sale of Fund shares
Average Annual Return:
1 Year	(10.60%)
5 Years	(0.95%)
10 Years	5.27%
(Columbia Acorn International Select A,C & I) | (Columbia Acorn International Select) | MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)
Average Annual Return:
1 Year	(12.14%)
5 Years	(4.72%)
10 Years	4.67%
(Columbia Acorn International Select A,C & I) | (Columbia Acorn International Select) | S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	(14.01%)
5 Years	(3.06%)
10 Years	8.41%
(Columbia Acorn International Select A,C & I) | (Columbia Acorn International Select) | Class A Shares
Average Annual Return:
1 Year	(15.28%)
5 Years	(1.13%)
10 Years	8.20%
(Columbia Acorn International Select A,C & I) | (Columbia Acorn International Select) | Class A Shares | returns after taxes on distributions
Average Annual Return:
1 Year	(15.64%)
5 Years	(1.47%)
10 Years	8.04%
(Columbia Acorn International Select A,C & I) | (Columbia Acorn International Select) | Class A Shares | returns after taxes on distributions and sale of Fund shares
Average Annual Return:
1 Year	(9.14%)
5 Years	(0.86%)
10 Years	7.38%
(Columbia Acorn International Select A,C & I) | (Columbia Acorn International Select) | Class C Shares
Average Annual Return:
1 Year	(11.69%)
5 Years	(0.75%)
10 Years	8.03%
(Columbia Acorn International Select A,C & I) | (Columbia Acorn International Select) | Class I Shares
Average Annual Return:
1 Year	(9.68%)
5 Years	0.43%
10 Years	9.24%
(Columbia Acorn International Select B) | (Columbia Acorn International Select) | MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)
Average Annual Return:
1 Year	(12.14%)
5 Years	(4.72%)
10 Years	4.67%
(Columbia Acorn International Select B) | (Columbia Acorn International Select) | S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	(14.01%)
5 Years	(3.06%)
10 Years	8.41%
(Columbia Acorn International Select B) | (Columbia Acorn International Select) | Class B Shares
Average Annual Return:
1 Year	(14.99%)
5 Years	(0.95%)
10 Years	8.14%
(Columbia Acorn International Select B) | (Columbia Acorn International Select) | Class B Shares | returns after taxes on distributions
Average Annual Return:
1 Year	(15.22%)
5 Years	(1.21%)
10 Years	8.04%
(Columbia Acorn International Select B) | (Columbia Acorn International Select) | Class B Shares | returns after taxes on distributions and sale of Fund shares
Average Annual Return:
1 Year	(9.13%)
5 Years	(0.69%)
10 Years	7.33%
(Columbia Acorn International Select Z) | (Columbia Acorn International Select) | MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)
Average Annual Return:
1 Year	(12.14%)
5 Years	(4.72%)
10 Years	4.67%
(Columbia Acorn International Select Z) | (Columbia Acorn International Select) | S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	(14.01%)
5 Years	(3.06%)
10 Years	8.41%
(Columbia Acorn International Select Z) | (Columbia Acorn International Select) | Class Z Shares
Average Annual Return:
1 Year	(9.76%)
5 Years	0.41%
10 Years	9.22%
(Columbia Acorn International Select Z) | (Columbia Acorn International Select) | Class Z Shares | returns after taxes on distributions
Average Annual Return:
1 Year	(10.24%)
5 Years	0.01%
10 Years	9.02%
(Columbia Acorn International Select Z) | (Columbia Acorn International Select) | Class Z Shares | returns after taxes on distributions and sale of Fund shares
Average Annual Return:
1 Year	(5.37%)
5 Years	0.45%
10 Years	8.31%
(Columbia Thermostat Fund A&C) | (Columbia Thermostat Fund) | S&P 500® Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	2.11%
5 Years	(0.25%)
Life of Fund	6.85%
Inception Date	Sep. 25, 2002
(Columbia Thermostat Fund A&C) | (Columbia Thermostat Fund) | Barclays U.S. Aggregate Bond Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	7.84%
5 Years	6.50%
Life of Fund	5.33%
Inception Date	Sep. 25, 2002
(Columbia Thermostat Fund A&C) | (Columbia Thermostat Fund) | 50-50 S&P 500/Barclays Capital Aggregate Bond (an equally weighted custom composite of the Fund's primary benchmarks for equity and debt securities, established by the Investment Manager; reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	5.28%
5 Years	3.54%
Life of Fund	6.43%
Inception Date	Sep. 25, 2002
(Columbia Thermostat Fund A&C) | (Columbia Thermostat Fund) | Lipper Flexible Portfolio Funds Index (reflects no deductions for taxes)
Average Annual Return:
1 Year	(1.16%)
5 Years	2.02%
Life of Fund	7.10%
Inception Date	Sep. 25, 2002
(Columbia Thermostat Fund A&C) | (Columbia Thermostat Fund) | Class A Shares
Average Annual Return:
1 Year	(1.41%)
5 Years	2.74%
Life of Fund	6.56%
Inception Date	Sep. 25, 2002
(Columbia Thermostat Fund A&C) | (Columbia Thermostat Fund) | Class A Shares | returns after taxes on distributions
Average Annual Return:
1 Year	(2.31%)
5 Years	1.77%
Life of Fund	5.42%
Inception Date	Sep. 25, 2002
(Columbia Thermostat Fund A&C) | (Columbia Thermostat Fund) | Class A Shares | returns after taxes on distributions and sale of Fund shares
Average Annual Return:
1 Year	(0.92%)
5 Years	1.85%
Life of Fund	5.18%
Inception Date	Sep. 25, 2002
(Columbia Thermostat Fund A&C) | (Columbia Thermostat Fund) | Class C Shares
Average Annual Return:
1 Year	2.87%
5 Years	3.19%
Life of Fund	6.45%
Inception Date	Sep. 25, 2002
(Columbia Thermostat Fund B) | (Columbia Thermostat Fund) | S&P 500® Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	2.11%
5 Years	(0.25%)
Life of Fund	6.85%
Inception Date	Sep. 25, 2002
(Columbia Thermostat Fund B) | (Columbia Thermostat Fund) | Barclays U.S. Aggregate Bond Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	7.84%
5 Years	6.50%
Life of Fund	5.33%
Inception Date	Sep. 25, 2002
(Columbia Thermostat Fund B) | (Columbia Thermostat Fund) | 50-50 S&P 500/Barclays Capital Aggregate Bond (an equally weighted custom composite of the Fund's primary benchmarks for equity and debt securities, established by the Investment Manager; reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	5.28%
5 Years	3.54%
Life of Fund	6.43%
Inception Date	Sep. 25, 2002
(Columbia Thermostat Fund B) | (Columbia Thermostat Fund) | Lipper Flexible Portfolio Funds Index (reflects no deductions for taxes)
Average Annual Return:
1 Year	(1.16%)
5 Years	2.02%
Life of Fund	7.10%
Inception Date	Sep. 25, 2002
(Columbia Thermostat Fund B) | (Columbia Thermostat Fund) | Class B Shares
Average Annual Return:
1 Year	(0.81%)
5 Years	3.10%
Life of Fund	6.65%
Inception Date	Sep. 25, 2002
(Columbia Thermostat Fund B) | (Columbia Thermostat Fund) | Class B Shares | returns after taxes on distributions
Average Annual Return:
1 Year	(1.53%)
5 Years	2.27%
Life of Fund	5.70%
Inception Date	Sep. 25, 2002
(Columbia Thermostat Fund B) | (Columbia Thermostat Fund) | Class B Shares | returns after taxes on distributions and sale of Fund shares
Average Annual Return:
1 Year	(0.53%)
5 Years	2.24%
Life of Fund	5.38%
Inception Date	Sep. 25, 2002
(Columbia Thermostat Fund Z) | (Columbia Thermostat Fund) | S&P 500® Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	2.11%
5 Years	(0.25%)
Life of Fund	6.85%
Inception Date	Sep. 25, 2002
(Columbia Thermostat Fund Z) | (Columbia Thermostat Fund) | Barclays U.S. Aggregate Bond Index (reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	7.84%
5 Years	6.50%
Life of Fund	5.33%
Inception Date	Sep. 25, 2002
(Columbia Thermostat Fund Z) | (Columbia Thermostat Fund) | 50-50 S&P 500/Barclays Capital Aggregate Bond (an equally weighted custom composite of the Fund's primary benchmarks for equity and debt securities, established by the Investment Manager; reflects no deductions for fees, expenses or taxes)
Average Annual Return:
1 Year	5.28%
5 Years	3.54%
Life of Fund	6.43%
Inception Date	Sep. 25, 2002
(Columbia Thermostat Fund Z) | (Columbia Thermostat Fund) | Lipper Flexible Portfolio Funds Index (reflects no deductions for taxes)
Average Annual Return:
1 Year	(1.16%)
5 Years	2.02%
Life of Fund	7.10%
Inception Date	Sep. 25, 2002
(Columbia Thermostat Fund Z) | (Columbia Thermostat Fund) | Class Z Shares
Average Annual Return:
1 Year	4.85%
5 Years	4.21%
Life of Fund	7.51%
Inception Date	Sep. 25, 2002
(Columbia Thermostat Fund Z) | (Columbia Thermostat Fund) | Class Z Shares | returns after taxes on distributions
Average Annual Return:
1 Year	3.80%
5 Years	3.12%
Life of Fund	6.26%
Inception Date	Sep. 25, 2002
(Columbia Thermostat Fund Z) | (Columbia Thermostat Fund) | Class Z Shares | returns after taxes on distributions and sale of Fund shares
Average Annual Return:
1 Year	3.15%
5 Years	3.06%
Life of Fund	5.97%
Inception Date	Sep. 25, 2002

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(Columbia Thermostat Fund B) | (Columbia Thermostat Fund)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Thermostat Fund)		Class B Shares (Columbia Thermostat Fund B)
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	[1]	5.00%

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Thermostat Fund)		Class B Shares (Columbia Thermostat Fund B)
Management fees		0.10%
Distribution and/or service (Rule 12b-1) fees		0.75%
Other expenses	[1]	0.52%
Acquired Fund Fees and Expenses		0.65%
Total annual Fund operating expenses	[2]	2.02%
Fee waivers and/or reimbursements	[3]	(0.37%)
Total annual Fund operating expenses after fee waivers and/or reimbursements		1.65%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class B shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire on April 30, 2013, they are only reflected in the 1 year example and the first year of the 3, 5 and 10 year examples.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Thermostat Fund) (USD $)	1 Year	3 Years	5 Years	10 Years
Class B Shares (Columbia Thermostat Fund B)	668	898	1,254	2,174

Expense Example, No Redemption (Columbia Thermostat Fund) (USD $)	1 Year	3 Years	5 Years	10 Years
Class B Shares (Columbia Thermostat Fund B)	168	598	1,054	2,174

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund will indirectly bear the expenses associated with portfolio turnover of the underlying Portfolio Funds in which the Fund invests. Each Portfolio Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A Portfolio Fund's higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when its shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 130% of the average value of its portfolio.

Principal Investment Strategies

The Fund pursues its investment objective by investing in other mutual funds. As a "fund of funds," under normal circumstances, the Fund allocates at least 95% of its net assets (stock/bond assets) among a selected group of stock and bond mutual funds (Portfolio Funds) according to the current level of Standard & Poor's (S&P) 500® Index. Generally, when the S&P 500® Index goes up in relation to predetermined ranges set by Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), the Fund sells a portion of its stock funds and invests more in the bond funds and when the S&P 500® Index goes down in relation to the ranges, the Fund increases its investment in the stock funds. Under normal circumstances, the Fund may invest up to 5% of net assets plus any cash received that day in cash, high quality short-term paper and government securities.

Many asset allocation funds typically move assets from stocks to bonds when the market goes up, and from bonds to stocks when the market goes down. Most asset allocation funds are run by sophisticated investment professionals, who make subjective decisions based on economic and financial data and complex graphs of market behavior. By contrast, the day-to-day investment decisions for the Fund are made according to a single predetermined rule. The temperature in your house is run by a single rule: your thermostat turns on the furnace if your house is too cold or turns on the air conditioner if your house is too warm. This Fund works the same way, so it is named Columbia Thermostat Fund.

Because the Fund invests according to a pre-set program, there is no need for subjective day-to-day management. Although another successful asset allocation strategy might do better than the Fund, the Fund is designed for those who doubt the wisdom of trying to "time" the market and are unsure of the long-term trend of the stock market. The Fund takes psychology out of investing; it avoids the temptation to buy more stocks because the stock market is currently going up or to sell stocks because the market is declining. The Fund operates continuously and substantially automatically, subject to periodic review of the pre-set program by the Investment Manager and the Fund's Board of Trustees. As described more fully below, the Investment Manager has the authority to review the structure and allocation ranges of the stock/bond allocation table and to make any changes considered appropriate.

The Investment Manager chooses the Portfolio Funds to provide participation in the major sectors of the stock and bond markets. If you believe that the stock market will tend to go up most of the time, then you should probably own a fully invested stock fund and use a buy-and-hold strategy. Buy-and-hold was an excellent strategy in the 1982-1999 bull market. However, there have been long periods in the past when buy-and-hold was not the best strategy, such as 1930-1954 and 1969-1981, when the market fluctuated but did not make significant new highs. The Fund may be a good investment choice for you if you believe that the market may fluctuate in a trading range for many years, that a remarkable bull market ended early in 2000 and that the market may not reach significant new highs for many years.

The Fund invests its stock/bond assets among the Portfolio Funds according to an asset allocation table. The current allocation table is set forth below.

Stock/Bond Allocation Table

                                      How the Fund will Invest the Stock/Bond Assets

                                      ----------------------------------------------



Level of the S and P 500(R) Index   	    Stock Percentage     Bond Percentage

---------------------------------           ----------------     ---------------

over 1750                                          10%                90%

over 1700 -- 1750                                  15%                85%

over 1650 -- 1700                                  20%                80%

over 1600 -- 1650                                  25%                75%

over 1550 -- 1600                                  30%                70%

over 1500 -- 1550                                  35%                65%

over 1450 -- 1500                                  40%                60%

over 1400 -- 1450                                  45%                55%

over 1350 -- 1400                                  50%                50%

over 1300 -- 1350                                  55%                45%

over 1250 -- 1300                                  60%                40%

over 1200 -- 1250                                  65%                35%

over 1150 -- 1200                                  70%                30%

over 1100 -- 1150                                  75%                25%

over 1050 -- 1100                                  80%                20%

over 1000 -- 1050                                  85%                15%

1000 and under                                     90%                10%

When the S&P 500® Index moves into a new band on the table, the Fund promptly will rebalance the stock/bond mix to reflect the new S&P 500® Index price level by redeeming shares of some Portfolio Funds and purchasing shares of other Portfolio Funds. The only exception will be a "31-day Rule"; in order to reduce taxable events, after the Fund has increased its percentage allocation to either stock funds or bond funds, it will not decrease that allocation for at least 31 days. Following a change in the Fund's stock/bond mix, if the S&P 500® Index remains within the same band for a while, normal market fluctuations will change the values of the Fund's holdings of stock Portfolio Funds and bond Portfolio Funds. The Investment Manager will invest cash flows from sales (or redemptions) of Fund shares to bring the stock/bond mix back toward the allocation percentages for that S&P 500® Index band. For example, if the S&P 500® Index is in the 1150-1200 band, and the value of the holdings of the stock Portfolio Funds has dropped to 68% of the value of the holdings of all Portfolio Funds, the Investment Manager would invest new cash in the stock Portfolio Funds (or cash for redemptions would come from the bond Portfolio Funds). If the 31-day Rule is in effect, the Investment Manager will invest new cash at the stock/bond percentage allocation as of the latest rebalancing.

As an illustrative example, suppose the following:

 		              Level of the 		           How the Fund will invest

Date		          S and P 500(R) Index                       the Stock/Bond Assets

--------        ---------------------------------------         --------------------------------

Nov. 1             We begin when the market is 1380                  50% stocks, 50% bonds

Dec. 1             The S and P 500(R) goes to 1401              rebalance 45% stocks, 55% bonds

Dec. 6           The S and P 500(R) drops back to 1390              no reversal for 31 days

Jan. 2              The S and P 500(R) is at 1352               rebalance 50% stocks, 50% bonds

Jan. 20            The S and P 500(R) drops to 1349             rebalance 55% stocks, 45% bonds



      The market has made a continuation move by going through a second action level,

          not a reversal move, so the 31-day Rule does not apply in this case.



Jan. 30            The S and P 500(R) goes up to 1355               no reversal for 31 days

Feb. 20              The S and P 500(R) is at 1360              rebalance 50% stocks, 50% bonds

The following table shows the seven stock Portfolio Funds and three bond Portfolio Funds that the Fund currently uses in its "fund of funds" structure and the current allocation percentage for each Portfolio Fund within the stock or bond category. As described more fully below, the Investment Manager may substitute or add additional Portfolio Funds at any time, including funds introduced after the date of this prospectus. The allocation percentage within each stock/bond category is achieved by rebalancing the investments within the category whenever the S&P 500® Index moves into a new band on the allocation table, subject to the 31-day Rule described above. The Fund does not liquidate its investment in one Portfolio Fund in order to invest in another Portfolio Fund except in connection with a rebalancing due to a move of the S&P 500® Index into a new band (or due to a change by the Investment Manager in the stock/bond allocation table to the Portfolio Funds or to the relative allocation among them). Until a subsequent rebalancing, the Fund's investments in, and redemptions from, the stock Portfolio Funds or the bond Portfolio Funds are allocated among the Portfolio Funds in a manner that will reduce any deviation of the relative values of the Fund's holdings of the Funds from the allocation percentages shown below.

Allocation of Stock/Bond Assets Within Asset Classes

Stock Funds                                   Type of Fund 	             Allocation

-------------------------------------  ------------------------------------  -----------

Columbia Acorn Fund                    Small/Mid-cap growth                          15%

Columbia Acorn Select                  Mid-cap growth                                10%

Columbia Acorn International           Small/Mid-cap international growth            20%

Columbia Dividend Income Fund          Large-cap value                               20%

Columbia Large Cap Enhanced Core Fund  Large-cap blend                               10%

Columbia Contrarian Core Fund          Large-cap blend                               15%

Columbia Select Large Cap Growth Fund  Large-cap growth                              10%

Total                                                                               100%



Bond Funds                                    Type of Fund 	             Allocation

-------------------------------------  ------------------------------------  -----------

Columbia Intermediate Bond Fund        Intermediate-term bonds                       50%

Columbia Income Opportunities Fund     High-yield bonds                              30%

Columbia U.S. Treasury Index Fund      U.S. Treasury notes/bonds                     20%

Total                                                                               100%

The Investment Manager has the authority to review the Portfolio Funds and the relative stock/bond allocation percentages among them and to make any changes considered appropriate.

Each of the Portfolio Funds is currently managed by the Investment Manager or its affiliates. The Fund does not pay any sales load on its purchases of shares of the Portfolio Funds. On an annual basis, or on an "emergency" basis if necessary, the Investment Manager reviews the structure, allocation percentages and Portfolio Funds and makes any changes considered appropriate. The Investment Manager typically addresses the following questions:

• Should the stock/bond allocation table be revised (perhaps because the stock market has made a long-term move outside of the bands set forth above)?
• Should there be a change in the Portfolio Funds or should there be a change in the percentage allocations among the stock/bond funds (perhaps because of a change of portfolio managers, change of investment style, change in relative valuation or a reorganization of a Portfolio Fund)?

Any such changes by the Investment Manager are expected to be infrequent.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Allocation Risk – The Fund uses an asset allocation strategy in pursuit of its investment objective. There is a risk that the Fund's allocation among asset classes or investments will cause the Fund's shares to lose value or cause the Fund to underperform other funds with similar investment objectives, or that the investments themselves will not produce the returns expected.

• Investing in Other Funds Risk – The performance of the underlying fund(s) in which the Fund invests could be adversely affected if other entities that invest in the same underlying fund(s) make relatively large investments or redemptions in the underlying fund(s). In addition, because the expenses and costs of the underlying fund(s) are shared by investors in the underlying fund, redemptions by other investors in the underlying fund could result in decreased economies of scale and increased operating expenses for the underlying fund. The Fund, and its shareholders, indirectly bear a portion of the expenses of the underlying fund(s). These transactions might also result in higher brokerage, tax or other costs for the Fund. This risk may be particularly important when one investor owns a substantial portion of any underlying fund. In addition, the Investment Manager has the authority to change the underlying fund(s) in which the Fund invests or to change the percentage of the Fund's investments allocated to each underlying fund. If an underlying fund pays fees to the Investment Manager or its affiliates, such as advisory fees, this could result in the Investment Manager having a potential conflict of interest in selecting the underlying fund(s) in which the Fund invests or in determining the percentage of the Fund's investments allocated to each underlying fund. In addition, the underlying funds are themselves subject to Investment Strategy Risk.

The Fund is subject indirectly to the following risks of the Portfolio Funds:

• Market Risk – Market risk refers to the possibility that the market values of securities that a Portfolio Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Portfolio Fund. Accordingly, an investment in a Portfolio Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Portfolio Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Interest Rate Risk – Debt securities are subject to interest rate risk. In general, if prevailing interest rates rise, the values of debt securities will tend to fall, and if interest rates fall, the values of debt securities will tend to rise. Changes in the value of a debt security usually will not affect the amount of income a Portfolio Fund receives from it but may affect the value of the Portfolio Fund's shares. Interest rate risk is generally greater for debt securities with longer maturities/durations.

• Credit Risk – Credit risk applies to most debt securities, but is generally less of a factor for obligations backed by the "full faith and credit" of the U.S. Government. A Portfolio Fund could lose money if the issuer of a debt security owned by the Fund is unable or perceived to be unable to pay interest or repay principal when it becomes due. Various factors could affect the issuer's actual or perceived willingness or ability to make timely interest or principal payments, including changes in the issuer's financial condition or in general economic conditions. Debt securities backed by an issuer's taxing authority may be subject to legal limits on the issuer's power to increase taxes or otherwise to raise revenue, or may be dependent on legislative appropriation or government aid. Certain debt securities are backed only by revenues derived from a particular project or source, rather than by an issuer's taxing authority, and thus may have a greater risk of default.

• Low and Below Investment Grade Securities Risk – Debt securities with the lowest investment grade rating (e.g., BBB by Standard & Poor's, a division of the McGraw-Hill Companies, Inc. (S&P), or Fitch, Inc. (Fitch) or Baa by Moody's Investors Service, Inc. (Moody's)), or that are below investment grade (which are commonly referred to as "junk bonds") (e.g., BB or below by S&P or Fitch or Ba by Moody's) and unrated securities of comparable quality are more speculative than securities with higher ratings and may experience greater price fluctuations. These securities tend to be more sensitive to credit risk than higher-rated securities, particularly during a downturn in the economy, which is more likely to weaken the ability of the issuers to make principal and interest payments on these securities. These securities typically pay a premium – a higher interest rate or yield – because of the increased risk of loss, including default. These securities also are generally less liquid than higher-rated securities. The securities ratings provided by Moody's, S&P and Fitch are based on analyses by these ratings agencies of the credit quality of the securities and may not take into account every risk related to whether interest or principal will be timely repaid.

• Value Securities Risk – Value securities are securities of companies that may have experienced, for example, adverse business, industry or other developments or may be subject to special risks that have caused the securities to be out of favor and, in turn, potentially undervalued. The market value of a portfolio security may not meet the Investment Manager's future value assessment of that security, or may decline. There is also a risk that it may take longer than expected for the value of these investments to rise to the believed value. In addition, value securities, at times, may not perform as well as growth securities or the stock market in general, and may be out of favor with investors for varying periods of time.

• Growth Securities Risk – Because growth securities typically trade at a higher multiple of earnings than other types of securities, the market values of growth securities may be more sensitive to changes in current or expected earnings than the market values of other types of securities. In addition, growth securities, at times, may not perform as well as value securities or the stock market in general, and may be out of favor with investors for varying periods of time.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Portfolio Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Portfolio Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Index Risk – U.S. Treasury Index Fund's value will generally decline when the performance of its targeted index declines. Because U.S. Treasury Index Fund is designed to track an index before fees and expenses, U.S. Treasury Index Fund cannot purchase other securities that may help offset declines in its index. In addition, because U.S. Treasury Index Fund may not hold all issues included in its index, may not always be fully invested, and bears advisory, administrative and other expenses and transaction costs in trading securities, U.S. Treasury Index Fund's performance may fail to match the performance of its targeted index, after taking expenses into account. It is not possible to invest directly in an index.

• U.S. Government Obligations Risk – While U.S. Treasury obligations are backed by the "full faith and credit" of the U.S. Government, such securities are nonetheless subject to credit risk (i.e., the risk that the U.S. Government may be, or may be perceived to be, unable or unwilling to honor its financial obligations, such as making payments). Securities issued or guaranteed by federal agencies or authorities and U.S. Government-sponsored instrumentalities or enterprises may or may not be backed by the full faith and credit of the U.S. Government. For example, securities issued by the Federal Home Loan Mortgage Corporation, the Federal National Mortgage Association and the Federal Home Loan Banks are neither insured nor guaranteed by the U.S. Government. These securities may be supported by the ability to borrow from the U.S. Treasury or only by the credit of the issuing agency, authority, instrumentality or enterprise and, as a result, are subject to greater credit risk than securities issued or guaranteed by the U.S. Treasury. Securities guaranteed by the Federal Deposit Insurance Corporation under its Temporary Liquidity Guarantee Program (TLGP) are subject to certain risks, including whether such securities will continue to trade in line with recent experience in relation to treasury and government agency securities in terms of yield spread and the volatility of such spread, as well as uncertainty as to how such securities will trade in the secondary market and whether that market will be liquid or illiquid. The TLGP is subject to change. See ABOUT THE FUNDS' INVESTMENTS - U.S. Government and Related Obligations in the Statement of Additional Information for more information.

• Derivatives Risk – Derivatives are financial contracts whose values are, for example, based on (or "derived" from) traditional securities (such as a stock or bond), assets (such as a commodity like gold or a foreign currency), reference rates (such as LIBOR) or market indices (such as the S&P 500® Index). Derivatives involve special risks and may result in losses or may limit a Portfolio Fund's potential gain from favorable market movements. Derivative strategies often involve leverage, which may exaggerate a loss, potentially causing a Portfolio Fund to lose more money than it would have lost had it invested in the underlying security or other asset. The values of derivatives may move in unexpected ways, especially in unusual market conditions, and may result in increased volatility, among other consequences. The use of derivatives may also increase the amount of taxes payable by shareholders holding shares in a taxable account. Other risks arise from a Portfolio Fund's potential inability to terminate or to sell derivative positions. A liquid secondary market may not always exist for the Portfolio Fund's derivative positions at times when the Portfolio Fund might wish to terminate or to sell such positions. Over-the-counter instruments (investments not traded on an exchange) may be illiquid, and transactions in derivatives traded in the over-the-counter market are subject to the risk that the other party will not meet its obligations. The use of derivatives also involves the risks of mispricing or improper valuation and that changes in the value of the derivative may not correlate perfectly with the underlying security, asset, reference rate or index. A Portfolio Fund also may not be able to find a suitable derivative transaction counterparty, and thus may be unable to engage in derivative transactions when it is deemed favorable to do so, or at all. U.S. federal legislation has recently been enacted that provides for new clearing, margin, reporting and registration requirements for participants in the derivatives market. While the ultimate impact is not yet clear, these changes could restrict and/or impose significant costs or other burdens upon the Fund's participation in derivatives transactions. For more information on the risks of derivative investments and strategies, see the Statement of Additional Information.

• Convertible Securities Risk – Certain Portfolio Funds invest in convertible securities, which are subject to the usual risks associated with debt securities, such as interest rate risk and credit risk. Convertible securities also react to changes in the value of the common stock into which they convert. Because the value of a convertible security can be influenced by both interest rates and the common stock's market movements, a convertible security generally is not as sensitive to interest rates as a similar debt security, and generally will not vary in value in response to other factors to the same extent as the underlying common stock. In the event of a liquidation of the issuing company, holders of convertible securities would typically be paid before the company's common stockholders but after holders of any senior debt obligations of the company. A Portfolio Fund may be forced to convert a convertible security before it otherwise would choose to do so, which may decrease the Portfolio Fund's return.

• Non-Diversified Mutual Fund Risk – If a Portfolio Fund is non-diversified, that Portfolio Fund generally may invest a greater percentage of its total assets in the securities of fewer issuers than may a "diversified" fund. This increases the risk that a change in the value of any one investment held by the non-diversified Portfolio Fund could affect the overall value of the Portfolio Fund more than it would affect that of a diversified fund holding a greater number of investments. Accordingly, a non-diversified Portfolio Fund's value will likely be more volatile than the value of more diversified funds. A Portfolio Fund that is non-diversified may not operate as a non-diversified fund at all times.

• Technology Sector Risk – Companies in the technology sector are subject to significant competitive pressures, such as aggressive pricing of their products or services, new market entrants, competition for market share, short product cycles due to an accelerated rate of technological developments and the potential for limited earnings and/or falling profit margins. These companies also face the risks that new services, equipment or technologies will not be accepted by consumers and businesses or will become rapidly obsolete. These factors can affect the profitability of technology companies and, as a result, the value of their securities. Also, patent protection is integral to the success of many companies in the technology sector, and profitability can be affected materially by, among other things, the cost of obtaining (or failing to obtain) patent approvals, the cost of litigating patent infringement and the loss of patent protection for products (which significantly increases pricing pressures and can materially reduce profitability with respect to such products). In addition, many technology companies have limited operating histories. Prices of these companies' securities historically have been more volatile than other securities, especially over the short term. Because certain Portfolio Funds invest a significant portion of their net assets in the equity securities of technology companies, a Portfolio Fund's price may be more volatile than a fund that is invested in a more diverse range of market sectors.

• Health Care Sector Risk - Companies in the health care sector are subject to extensive government regulation. Their profitability can be affected significantly and adversely by restrictions on government reimbursement for medical expenses, government approval of medical products and services, competitive pricing pressures, an increased emphasis on outpatient and other alternative services and other factors. Patent protection is integral to the success of companies in the health care sector, and profitability can be affected materially by, among other things, the cost of obtaining (or failing to obtain) patent approvals, the cost of litigating patent infringement and the loss of patent protection for medical products (which significantly increases pricing pressures and can materially reduce profitability with respect to such products). Companies in the health care sector also potentially are subject to extensive product liability and other similar litigation. Companies in the health care sector are affected by the rising cost of medical products and services, and the effects of such rising costs can be particularly pronounced for companies that are dependent on a relatively limited number of products or services. Medical products also frequently become obsolete due to industry innovation or other causes. Because certain Portfolio Funds invest a significant portion of their net assets in the equity securities of health care companies, a Portfolio Fund's price may be more volatile than a fund that is invested in a more diverse range of market sectors.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The inception date for the Fund's Class B shares is March 3, 2003. The returns shown for this share class include the returns of the Fund's Class Z shares (adjusted to reflect the higher class-related operating expenses of Class B shares) for periods from the inception date of Class Z shares (September 25, 2002) to the inception date of Class B shares. Except for differences in expenses and sales charges, Class B shares have annual returns substantially similar to those of Class Z shares, which are not offered in this prospectus, because all classes of the Fund's shares invest in the same portfolio of securities.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class B shares has varied from year to year.

Year by Year Total Return (%) as of December 31 Each Year

^[1]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    19.07%

Worst:   4th quarter 2008:   -19.47%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns for each period with those of the S&P 500® Index, the Fund's primary benchmark for equity securities, the Barclays U.S. Aggregate Bond Index, the Fund's primary benchmark for debt securities, the Lipper Flexible Portfolio Funds Index and a 50/50 Blended Benchmark. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. The Barclays U.S. Aggregate Bond Index is a market value-weighted index that tracks the daily price, coupon, pay-downs, and total return performance of fixed-rate, publicly placed, dollar-denominated, and non-convertible investment grade debt issues with at least $250 million par amount outstanding and with at least one year to final maturity. The Lipper Flexible Portfolio Funds Index is an equal-weighted index of the 30 largest mutual funds within the Flexible Portfolio fund classification, as defined by Lipper, and shows how the Fund's performance compares with the returns of an index of funds with similar investment objectives. The 50/50 Blended Benchmark was established by the Investment Manager to show how the Fund's performance compares to an equally weighted custom composite of the Fund's primary equity and primary debt benchmarks, the S&P 500® Index and the Barclays U.S. Aggregate Bond Index, respectively. The percentage of the Fund's assets allocated to underlying stock and bond Portfolio Funds will vary, and accordingly the composition of the Fund's portfolio will not always reflect the composition of the 50/50 Blended Benchmark.

Average Annual Total Returns (Columbia Thermostat Fund) (Columbia Thermostat Fund B)	Inception Date	1 Year	5 Years	Life of Fund
Class B Shares	Sep. 25, 2002	(0.81%)	3.10%	6.65%
Class B Shares returns after taxes on distributions	Sep. 25, 2002	(1.53%)	2.27%	5.70%
Class B Shares returns after taxes on distributions and sale of Fund shares	Sep. 25, 2002	(0.53%)	2.24%	5.38%
S&P 500® Index (reflects no deductions for fees, expenses or taxes)	Sep. 25, 2002	2.11%	(0.25%)	6.85%
Barclays U.S. Aggregate Bond Index (reflects no deductions for fees, expenses or taxes)	Sep. 25, 2002	7.84%	6.50%	5.33%
Lipper Flexible Portfolio Funds Index (reflects no deductions for taxes)	Sep. 25, 2002	(1.16%)	2.02%	7.10%
50-50 S&P 500/Barclays Capital Aggregate Bond (an equally weighted custom composite of the Fund's primary benchmarks for equity and debt securities, established by the Investment Manager; reflects no deductions for fees, expenses or taxes)	Sep. 25, 2002	5.28%	3.54%	6.43%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

[1] This charge decreases over time. See About Class B Shares - Sales Charges and Commissions for details.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[2] Total annual Fund operating expenses include the annualized average weighted fees and expenses of acquired funds (underlying Portfolio Funds). As a result, the amount shown is higher than the ratio of expenses to average net assets included in Financial Highlights, which reflects only those expenses paid directly by the Fund.

[3] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that ordinary operating expenses (excluding distribution and service fees, interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies) do not exceed the annual rate of 0.25% of the Fund's average daily net assets, through April 30, 2013. The figure shown here is the amount of expected waivers and/or reimbursements. This fee and expense arrangement may only be modified or amended with approval from all parties to such arrangement, including the Fund and the Investment Manager.

[1] Year-to-date return as of March 31, 2012: 8.06%

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(Columbia Acorn Fund Z) | (Columbia Acorn Fund)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn Fund)	Class Z Shares (Columbia Acorn Fund Z)
Maximum sales charge (load) imposed on purchases, as a % of offering price	none
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn Fund)		Class Z Shares (Columbia Acorn Fund Z)
Management fees		0.64%
Distribution and/or service (Rule 12b-1) fees		none
Other expenses	[1]	0.13%
Total annual Fund operating expenses		0.77%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class Z shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn Fund) (USD $)	1 Year	3 Years	5 Years	10 Years
Class Z Shares (Columbia Acorn Fund Z)	79	246	428	954

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 18% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion. Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Brazil).

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class Z shares has varied from year to year.

Year by Year Total Return (%) as of December 31 Each Year

^[1]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    20.90%

Worst:   4th quarter 2008:   -25.11%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns for each period with those of the Russell 2500 Index, the Fund's primary benchmark, the Standard & Poor's (S&P) 500® Index and the Russell 2000 Index. The Russell 2500 Index measures the performance of the 2,500 smallest companies in the Russell 3000 Index, which represents approximately 17% of the total market capitalization of the Russell 3000 Index. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in small and mid-sized companies, the comparison to the S&P 500® Index is presented to show performance against a widely recognized market index. The Russell 2000 Index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index. The Russell 2000 Index shows how the Fund's performance compares to a widely recognized broad based index of companies with somewhat lower capitalization than the Fund's primary benchmark.

Average Annual Total Returns (Columbia Acorn Fund) (Columbia Acorn Fund Z)	1 Year	5 Years	10 Years
Class Z Shares	(4.61%)	2.12%	8.24%
Class Z Shares returns after taxes on distributions	(5.23%)	1.58%	7.66%
Class Z Shares returns after taxes on distributions and sale of Fund shares	(2.13%)	1.81%	7.25%
Russell 2500 Index (reflects no deductions for fees, expenses or taxes)	(2.51%)	1.24%	6.57%
S&P 500® Index (reflects no deductions for fees, expenses or taxes)	2.11%	(0.25%)	2.92%
Russell 2000 Index (reflects no deductions for fees, expenses or taxes)	(4.18%)	0.15%	5.62%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] Year-to-date return as of March 31, 2012: 15.49%

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(Columbia Acorn Select B) | (Columbia Acorn Select)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn Select)		Class B Shares (Columbia Acorn Select B)
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	[1]	5.00%

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn Select)		Class B Shares (Columbia Acorn Select B)
Management fees		0.82%
Distribution and/or service (Rule 12b-1) fees		0.75%
Other expenses	[1]	0.48%
Total annual Fund operating expenses		2.05%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class B shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn Select) (USD $)	1 Year	3 Years	5 Years	10 Years
Class B Shares (Columbia Acorn Select B)	708	943	1,303	2,200

Expense Example, No Redemption (Columbia Acorn Select) (USD $)	1 Year	3 Years	5 Years	10 Years
Class B Shares (Columbia Acorn Select B)	208	643	1,103	2,200

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 21% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of companies with market capitalizations under $20 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $20 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $20 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $20 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $20 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Colombia).

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Fund may also invest in companies that the Investment Manager believes have good operational fundamentals but that the Investment Manager believes are undervalued due to negative investor sentiment related to company-specific or market-related conditions. Investments in turnaround and development stage companies may also be made when the Investment Manager believes potential returns outweigh risks of losses.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Opportunistic Investing Risk - Undervalued securities involve the risk that they may never reach their expected full market value, either because the market fails to recognize the security's intrinsic worth or the expected value was misgauged. Undervalued securities also may decline in price even though the Investment Manager believes they are already undervalued. Turnaround companies may never improve their fundamentals, may take much longer than expected to improve, or may improve much less than expected. Development stage companies could fail to develop and deplete their assets, resulting in large percentage losses.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class B shares has varied from year to year.

Year by Year Total Return (%) as of December 31 Each Year

^[1]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    27.78%

Worst:   4th quarter 2008:   -30.26%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns for each period with those of the Standard & Poor's (S&P) MidCap 400® Index, the Fund's primary benchmark, and the S&P 500® Index. The S&P MidCap 400® Index is a market value-weighted index that tracks the performance of 400 mid-cap U.S. companies. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in companies with market capitalizations under $20 billion at the time of investment, the comparison to the S&P 500® Index is presented to show performance against a widely recognized market index.

Average Annual Total Returns (Columbia Acorn Select) (Columbia Acorn Select B)	1 Year	5 Years	10 Years
Class B Shares	(21.22%)	(2.36%)	5.00%
Class B Shares returns after taxes on distributions	(21.49%)	(2.58%)	4.77%
Class B Shares returns after taxes on distributions and sale of Fund shares	(13.77%)	(2.00%)	4.36%
S&P MidCap 400® Index (reflects no deductions for fees, expenses or taxes)	(1.73%)	3.32%	7.04%
S&P 500® Index (reflects no deductions for fees, expenses or taxes)	2.11%	(0.25%)	2.92%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

[1] This charge decreases over time. See About Class B Shares - Sales Charges and Commissions for details.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] Year-to-date return as of March 31, 2012: 17.48%

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(Columbia Acorn Select A,C & I) | (Columbia Acorn Select)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds. More information about these and other discounts is available from your financial advisor, in the Choosing a Share Class section beginning on page 18 of this prospectus and in Appendix D to the Statement of Additional Information under Sales Charge Waivers beginning on page D-1.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn Select A,C & I) (Columbia Acorn Select)	Class A Shares		Class C Shares		Class I Shares
Maximum sales charge (load) imposed on purchases, as a % of offering price	5.75%
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[1]	1.00%	[2]

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn Select A,C & I) (Columbia Acorn Select)		Class A Shares	Class C Shares	Class I Shares
Management fees		0.82%	0.82%	0.82%
Distribution and/or service (Rule 12b-1) fees		0.25%	1.00%	none
Other expenses	[1]	0.28%	0.35%	0.09%
Total annual Fund operating expenses		1.35%	2.17%	0.91%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class A, Class C or Class I shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn Select) (Columbia Acorn Select A,C & I) (USD $)	1 Year	3 Years	5 Years	10 Years
Class A Shares	705	978	1,272	2,105
Class C Shares	320	679	1,164	2,503
Class I Shares	93	290	504	1,120

Expense Example, No Redemption (Columbia Acorn Select) (USD $)	1 Year	3 Years	5 Years	10 Years
Class C Shares (Columbia Acorn Select A,C & I)	220	679	1,164	2,503

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 21% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of companies with market capitalizations under $20 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $20 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $20 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $20 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $20 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Colombia).

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Fund may also invest in companies that the Investment Manager believes have good operational fundamentals but that the Investment Manager believes are undervalued due to negative investor sentiment related to company-specific or market-related conditions. Investments in turnaround and development stage companies may also be made when the Investment Manager believes potential returns outweigh risks of losses.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Opportunistic Investing Risk - Undervalued securities involve the risk that they may never reach their expected full market value, either because the market fails to recognize the security's intrinsic worth or the expected value was misgauged. Undervalued securities also may decline in price even though the Investment Manager believes they are already undervalued. Turnaround companies may never improve their fundamentals, may take much longer than expected to improve, or may improve much less than expected. Development stage companies could fail to develop and deplete their assets, resulting in large percentage losses.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The inception date for the Fund's Class I shares is September 27, 2010. The returns shown for Class I shares include the returns of the Fund's Class Z shares for periods prior to the inception date of Class I shares. Except for differences in expenses, Class I shares have annual returns substantially similar to those of Class Z shares, which are not offered in this prospectus, because all classes of the Fund's shares invest in the same portfolio of securities.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class A shares has varied from year to year. These returns do not reflect deductions of sales charges, if any, paid by investors and would be lower if they did.

Year by Year Total Return (%) as of December 31 Each Year

^[1]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    28.01%

Worst:   4th quarter 2008:   -30.17%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns for each period with those of the Standard & Poor's (S&P) MidCap 400® Index, the Fund's primary benchmark, and the S&P 500® Index. The S&P MidCap 400® Index is a market value-weighted index that tracks the performance of 400 mid-cap U.S. companies. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in companies with market capitalizations under $20 billion at the time of investment, the comparison to the S&P 500® Index is presented to show performance against a widely recognized market index.

Average Annual Total Returns (Columbia Acorn Select) (Columbia Acorn Select A,C & I)	1 Year	5 Years	10 Years
Class A Shares	(21.43%)	(2.52%)	5.07%
Class A Shares returns after taxes on distributions	(21.83%)	(2.76%)	4.82%
Class A Shares returns after taxes on distributions and sale of Fund shares	(13.89%)	(2.16%)	4.40%
Class C Shares	(18.09%)	(2.15%)	4.89%
Class I Shares	(16.25%)	(1.03%)	6.07%
S&P MidCap 400® Index (reflects no deductions for fees, expenses or taxes)	(1.73%)	3.32%	7.04%
S&P 500® Index (reflects no deductions for fees, expenses or taxes)	2.11%	(0.25%)	2.92%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown only for Class A shares and will vary for other share classes.

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

[1] Contingent deferred sales charges (CDSC) on certain investments of between $1 million and $50 million redeemed within 18 months of purchase, charged as follows: 1.00% CDSC if redeemed within 12 months of purchase, and 0.50% CDSC if redeemed more than 12, but less than 18, months of purchase, with certain limited exceptions.

[2] This charge applies to investors who buy Class C shares and redeem them within one year of purchase, with certain limited exceptions.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] Year-to-date return as of March 31, 2012: 17.65%

XML

Label

Element

Value

Risk/Return:

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Document Type

dei_DocumentType

485BPOS

Document Period End Date

dei_DocumentPeriodEndDate

Dec. 31, 2011

Registrant Name

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Columbia Acorn Trust

Central Index Key

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0000002110

Amendment Flag

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false

Document Creation Date

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Apr. 27, 2012

Document Effective Date

dei_DocumentEffectiveDate

May 01, 2012

Prospectus Date

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May 01, 2012

(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund)

Risk/Return:

rr_RiskReturnAbstract

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation.

Expense [Heading]

rr_ExpenseHeading

Fees and Expenses of the Fund

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds. More information about these and other discounts is available from your financial advisor, in the Choosing a Share Class section beginning on page 17 of this prospectus and in Appendix D to the Statement of Additional Information under Sales Charge Waivers beginning on page D-1.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 18% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

18.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class A, Class C or Class I shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example Closing [Text Block]

rr_ExpenseExampleClosingTextBlock

Remember this is an example only. Your actual costs may be higher or lower.

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion. Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Brazil).

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Risk [Heading]

rr_RiskHeading

Principal Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment. Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Performance Information

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The inception date for the Fund's Class I shares is September 27, 2010. The returns shown for Class I shares include the returns of the Fund's Class Z shares for periods prior to the inception date of Class I shares. Except for differences in expenses, Class I shares have annual returns substantially similar to those of Class Z shares, which are not offered in this prospectus, because all classes of the Fund's shares invest in the same portfolio of securities.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart below shows you how the performance of the Fund's Class A shares has varied from year to year.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800.345.6611

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.columbiamanagement.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Year by Year Total Return (%) as of December 31 Each Year

^[14]

Bar Chart Narrative [Text Block]

rr_BarChartNarrativeTextBlock

The bar chart below shows you how the performance of the Fund's Class A shares has varied from year to year. These returns do not reflect deductions of sales charges, if any, paid by investors and would be lower if they did.

Bar Chart Does Not Reflect Sales Loads [Text]

rr_BarChartDoesNotReflectSalesLoads

These returns do not reflect deductions of sales charges, if any, paid by investors and would be lower if they did.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    20.87%

Worst:   4th quarter 2008:   -25.19%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Return as of December 31, 2011

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

The after-tax returns are shown only for Class A shares and will vary for other share classes.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

The table compares the Fund's returns for each period with those of the Russell 2500 Index, the Fund's primary benchmark, the Standard & Poor's (S&P) 500® Index and the Russell 2000 Index. The Russell 2500 Index measures the performance of the 2,500 smallest companies in the Russell 3000 Index, which represents approximately 17% of the total market capitalization of the Russell 3000 Index. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in small and mid-sized companies, the comparison to the S&P 500® Index is presented to show performance against a widely recognized market index. The Russell 2000 Index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index. The Russell 2000 Index shows how the Fund's performance compares to a widely recognized broad based index of companies with somewhat lower capitalization than the Fund's primary benchmark.

Performance Table Closing [Text Block]

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The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown only for Class A shares and will vary for other share classes.

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund) | Russell 2500 Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(2.51%)

5 Years

rr_AverageAnnualReturnYear05

1.24%

10 Years

rr_AverageAnnualReturnYear10

6.57%

(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund) | S&P 500® Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

2.11%

5 Years

rr_AverageAnnualReturnYear05

(0.25%)

10 Years

rr_AverageAnnualReturnYear10

2.92%

(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund) | Russell 2000 Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(4.18%)

5 Years

rr_AverageAnnualReturnYear05

0.15%

10 Years

rr_AverageAnnualReturnYear10

5.62%

(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund) | Class A Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[1]

Management fees

rr_ManagementFeesOverAssets

0.64%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.22%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.11%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

682

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

908

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,151

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,849

Annual Return 2002

rr_AnnualReturn2002

(13.82%)

Annual Return 2003

rr_AnnualReturn2003

44.85%

Annual Return 2004

rr_AnnualReturn2004

21.05%

Annual Return 2005

rr_AnnualReturn2005

12.76%

Annual Return 2006

rr_AnnualReturn2006

14.13%

Annual Return 2007

rr_AnnualReturn2007

7.39%

Annual Return 2008

rr_AnnualReturn2008

(38.72%)

Annual Return 2009

rr_AnnualReturn2009

39.26%

Annual Return 2010

rr_AnnualReturn2010

25.61%

Annual Return 2011

rr_AnnualReturn2011

(4.91%)

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-date return as of March 31, 2012: 15.43%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

15.43%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

2nd quarter 2009:

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

20.87%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

4th quarter 2008:

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(25.19%)

1 Year

rr_AverageAnnualReturnYear01

(10.36%)

5 Years

rr_AverageAnnualReturnYear05

0.62%

10 Years

rr_AverageAnnualReturnYear10

7.21%

(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund) | Class A Shares | returns after taxes on distributions

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(10.94%)

5 Years

rr_AverageAnnualReturnYear05

0.10%

10 Years

rr_AverageAnnualReturnYear10

6.65%

(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund) | Class A Shares | returns after taxes on distributions and sale of Fund shares

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(5.94%)

5 Years

rr_AverageAnnualReturnYear05

0.53%

10 Years

rr_AverageAnnualReturnYear10

6.32%

(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund) | Class C Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[2]

Management fees

rr_ManagementFeesOverAssets

0.64%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other expenses

rr_OtherExpensesOverAssets

0.30%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.94%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

297

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

609

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,047

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,264

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

197

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

609

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

1,047

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

2,264

1 Year

rr_AverageAnnualReturnYear01

(6.53%)

5 Years

rr_AverageAnnualReturnYear05

1.02%

10 Years

rr_AverageAnnualReturnYear10

7.04%

(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund) | Class I Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

Management fees

rr_ManagementFeesOverAssets

0.64%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.07%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

0.71%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

73

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

227

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

395

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

883

1 Year

rr_AverageAnnualReturnYear01

(4.57%)

5 Years

rr_AverageAnnualReturnYear05

2.14%

10 Years

rr_AverageAnnualReturnYear10

8.25%

(Columbia Acorn Fund B) | (Columbia Acorn Fund)

Risk/Return:

rr_RiskReturnAbstract

Objective [Heading]

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Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation.

Expense [Heading]

rr_ExpenseHeading

Fees and Expenses of the Fund

Expense Narrative [Text Block]

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This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 18% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

18.00%

Expense Example [Heading]

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Example

Expense Example Narrative [Text Block]

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The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class B shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example Closing [Text Block]

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Remember this is an example only. Your actual costs may be higher or lower.

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion. Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Brazil).

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Risk [Heading]

rr_RiskHeading

Principal Risks

Risk Narrative [Text Block]

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• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Bar Chart and Performance Table [Heading]

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Performance Information

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart below shows you how the performance of the Fund's Class B shares has varied from year to year.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800.345.6611

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.columbiamanagement.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Year by Year Total Return (%) as of December 31 Each Year

^[15]

Bar Chart Narrative [Text Block]

rr_BarChartNarrativeTextBlock

The bar chart below shows you how the performance of the Fund's Class B shares has varied from year to year.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    20.64%

Worst:   4th quarter 2008:   -25.33%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Return as of December 31, 2011

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

The table compares the Fund's returns for each period with those of the Russell 2500 Index, the Fund's primary benchmark, the Standard & Poor's (S&P) 500® Index and the Russell 2000 Index. The Russell 2500 Index measures the performance of the 2,500 smallest companies in the Russell 3000 Index, which represents approximately 17% of the total market capitalization of the Russell 3000 Index. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in small and mid-sized companies, the comparison to the S&P 500® Index is presented to show performance against a widely recognized market index. The Russell 2000 Index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index. The Russell 2000 Index shows how the Fund's performance compares to a widely recognized broad based index of companies with somewhat lower capitalization than the Fund's primary benchmark.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn Fund B) | (Columbia Acorn Fund) | Russell 2500 Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(2.51%)

5 Years

rr_AverageAnnualReturnYear05

1.24%

10 Years

rr_AverageAnnualReturnYear10

6.57%

(Columbia Acorn Fund B) | (Columbia Acorn Fund) | S&P 500® Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

2.11%

5 Years

rr_AverageAnnualReturnYear05

(0.25%)

10 Years

rr_AverageAnnualReturnYear10

2.92%

(Columbia Acorn Fund B) | (Columbia Acorn Fund) | Russell 2000 Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(4.18%)

5 Years

rr_AverageAnnualReturnYear05

0.15%

10 Years

rr_AverageAnnualReturnYear10

5.62%

(Columbia Acorn Fund B) | (Columbia Acorn Fund) | Class B Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

5.00%

^[3]

Management fees

rr_ManagementFeesOverAssets

0.64%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.75%

Other expenses

rr_OtherExpensesOverAssets

0.42%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.81%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

684

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

869

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,180

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,943

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

184

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

569

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

980

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

1,943

Annual Return 2002

rr_AnnualReturn2002

(14.37%)

Annual Return 2003

rr_AnnualReturn2003

43.89%

Annual Return 2004

rr_AnnualReturn2004

20.15%

Annual Return 2005

rr_AnnualReturn2005

11.98%

Annual Return 2006

rr_AnnualReturn2006

13.43%

Annual Return 2007

rr_AnnualReturn2007

6.76%

Annual Return 2008

rr_AnnualReturn2008

(39.11%)

Annual Return 2009

rr_AnnualReturn2009

38.37%

Annual Return 2010

rr_AnnualReturn2010

24.81%

Annual Return 2011

rr_AnnualReturn2011

(5.34%)

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-date return as of March 31, 2012: 15.25%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

15.25%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

2nd quarter 2009:

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

20.64%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

4th quarter 2008:

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(25.33%)

1 Year

rr_AverageAnnualReturnYear01

(9.86%)

5 Years

rr_AverageAnnualReturnYear05

0.89%

10 Years

rr_AverageAnnualReturnYear10

7.17%

(Columbia Acorn Fund B) | (Columbia Acorn Fund) | Class B Shares | returns after taxes on distributions

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(10.50%)

5 Years

rr_AverageAnnualReturnYear05

0.33%

10 Years

rr_AverageAnnualReturnYear10

6.59%

(Columbia Acorn Fund B) | (Columbia Acorn Fund) | Class B Shares | returns after taxes on distributions and sale of Fund shares

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(5.51%)

5 Years

rr_AverageAnnualReturnYear05

0.76%

10 Years

rr_AverageAnnualReturnYear10

6.29%

(Columbia Acorn Fund Z) | (Columbia Acorn Fund)

Risk/Return:

rr_RiskReturnAbstract

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation.

Expense [Heading]

rr_ExpenseHeading

Fees and Expenses of the Fund

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 18% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

18.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class Z shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example Closing [Text Block]

rr_ExpenseExampleClosingTextBlock

Remember this is an example only. Your actual costs may be higher or lower.

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion. Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Brazil).

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Risk [Heading]

rr_RiskHeading

Principal Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Performance Information

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart below shows you how the performance of the Fund's Class Z shares has varied from year to year.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800.345.6611

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.columbiamanagement.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Year by Year Total Return (%) as of December 31 Each Year

^[16]

Bar Chart Narrative [Text Block]

rr_BarChartNarrativeTextBlock

The bar chart below shows you how the performance of the Fund's Class Z shares has varied from year to year.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    20.90%

Worst:   4th quarter 2008:   -25.11%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Return as of December 31, 2011

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

The table compares the Fund's returns for each period with those of the Russell 2500 Index, the Fund's primary benchmark, the Standard & Poor's (S&P) 500® Index and the Russell 2000 Index. The Russell 2500 Index measures the performance of the 2,500 smallest companies in the Russell 3000 Index, which represents approximately 17% of the total market capitalization of the Russell 3000 Index. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in small and mid-sized companies, the comparison to the S&P 500® Index is presented to show performance against a widely recognized market index. The Russell 2000 Index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index. The Russell 2000 Index shows how the Fund's performance compares to a widely recognized broad based index of companies with somewhat lower capitalization than the Fund's primary benchmark.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn Fund Z) | (Columbia Acorn Fund) | Russell 2500 Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(2.51%)

5 Years

rr_AverageAnnualReturnYear05

1.24%

10 Years

rr_AverageAnnualReturnYear10

6.57%

(Columbia Acorn Fund Z) | (Columbia Acorn Fund) | S&P 500® Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

2.11%

5 Years

rr_AverageAnnualReturnYear05

(0.25%)

10 Years

rr_AverageAnnualReturnYear10

2.92%

(Columbia Acorn Fund Z) | (Columbia Acorn Fund) | Russell 2000 Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(4.18%)

5 Years

rr_AverageAnnualReturnYear05

0.15%

10 Years

rr_AverageAnnualReturnYear10

5.62%

(Columbia Acorn Fund Z) | (Columbia Acorn Fund) | Class Z Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

none

Management fees

rr_ManagementFeesOverAssets

0.64%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.13%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

0.77%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

79

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

246

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

428

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

954

Annual Return 2002

rr_AnnualReturn2002

(13.31%)

Annual Return 2003

rr_AnnualReturn2003

45.68%

Annual Return 2004

rr_AnnualReturn2004

21.51%

Annual Return 2005

rr_AnnualReturn2005

13.11%

Annual Return 2006

rr_AnnualReturn2006

14.45%

Annual Return 2007

rr_AnnualReturn2007

7.69%

Annual Return 2008

rr_AnnualReturn2008

(38.55%)

Annual Return 2009

rr_AnnualReturn2009

39.65%

Annual Return 2010

rr_AnnualReturn2010

26.00%

Annual Return 2011

rr_AnnualReturn2011

(4.61%)

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-date return as of March 31, 2012: 15.49%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

15.49%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

2nd quarter 2009:

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

20.90%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

4th quarter 2008:

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(25.11%)

1 Year

rr_AverageAnnualReturnYear01

(4.61%)

5 Years

rr_AverageAnnualReturnYear05

2.12%

10 Years

rr_AverageAnnualReturnYear10

8.24%

(Columbia Acorn Fund Z) | (Columbia Acorn Fund) | Class Z Shares | returns after taxes on distributions

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(5.23%)

5 Years

rr_AverageAnnualReturnYear05

1.58%

10 Years

rr_AverageAnnualReturnYear10

7.66%

(Columbia Acorn Fund Z) | (Columbia Acorn Fund) | Class Z Shares | returns after taxes on distributions and sale of Fund shares

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(2.13%)

5 Years

rr_AverageAnnualReturnYear05

1.81%

10 Years

rr_AverageAnnualReturnYear10

7.25%

(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International)

Risk/Return:

rr_RiskReturnAbstract

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation.

Expense [Heading]

rr_ExpenseHeading

Fees and Expenses of the Fund

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds. More information about these and other discounts is available from your financial advisor, in the Choosing a Share Class section beginning on page 19 of this prospectus and in Appendix D to the Statement of Additional Information under Sales Charge Waivers beginning on page D-1.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

2013-08-14

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 32% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

32.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class A, Class C, Class I, Class R or Class R5 shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example Closing [Text Block]

rr_ExpenseExampleClosingTextBlock

Remember this is an example only. Your actual costs may be higher or lower.

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 75% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Brazil).

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Risk [Heading]

rr_RiskHeading

Principal Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Performance Information

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The inception date for the Fund's Class I shares is September 27, 2010 and the inception date for the Fund's Class R and R5 shares is August 2, 2011. The returns shown for Class I, Class R and Class R5 shares each include the returns of the Fund's Class Z shares (adjusted to reflect the higher class-related operating expenses of such classes, where applicable) for periods prior to the inception date of each class. Except for differences in expenses, these classes of shares each have annual returns substantially similar to those of Class Z shares, which are not offered in this prospectus, because all classes of the Fund's shares invest in the same portfolio of securities.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart below shows you how the performance of the Fund's Class A shares has varied from year to year.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800.345.6611

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.columbiamanagement.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Year by Year Total Return (%) as of December 31 Each Year

^[17]

Bar Chart Narrative [Text Block]

rr_BarChartNarrativeTextBlock

The bar chart below shows you how the performance of the Fund's Class A shares has varied from year to year. These returns do not reflect deductions of sales charges, if any, paid by investors and would be lower if they did.

Bar Chart Does Not Reflect Sales Loads [Text]

rr_BarChartDoesNotReflectSalesLoads

These returns do not reflect deductions of sales charges, if any, paid by investors and would be lower if they did.

Bar Chart Closing [Text Block]

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Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    33.20%

Worst:   3rd quarter 2008:   -23.79%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Return as of December 31, 2011

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

The after-tax returns are shown only for Class A shares and will vary for other share classes.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

The table compares the Fund's returns, for each period, with those of the Standard & Poor's (S&P) Global Ex-U.S. Between $500 Million and $5 Billion® Index, the Fund's primary benchmark, the S&P Global Ex-U.S. SmallCap® Index and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Global Ex-U.S. Between $500 Million and $5 Billion® Index is a subset of the broad market selected by the index sponsor that represents the mid- and small-cap developed and emerging markets, excluding the United States. The S&P Global Ex-U.S. SmallCap® Index is an unmanaged index consisting of the bottom 20% of institutionally investable capital of developed and emerging countries, excluding the United States. The performance of the S&P Global Ex-U.S. Small Cap® Index is provided to show how the Fund's performance compares to foreign market performance with a similar geographic distribution and wider market cap range than the Fund's primary benchmark. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund's performance compares to a widely recognized broad based index of foreign market performance.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown only for Class A shares and will vary for other share classes.

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | S&P Global Ex-U.S. Between $500 Million and $5 Billion® Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(16.94%)

5 Years

rr_AverageAnnualReturnYear05

(0.58%)

10 Years

rr_AverageAnnualReturnYear10

11.10%

(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | S&P Global Ex-U.S. SmallCap® Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(17.40%)

5 Years

rr_AverageAnnualReturnYear05

(2.14%)

10 Years

rr_AverageAnnualReturnYear10

10.33%

(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(12.14%)

5 Years

rr_AverageAnnualReturnYear05

(4.72%)

10 Years

rr_AverageAnnualReturnYear10

4.67%

(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | Class A Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[1]

Management fees

rr_ManagementFeesOverAssets

0.76%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.38%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.39%

Fee waivers and/or reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.04%)

^[7]

Total annual Fund operating expenses after fee waivers and/or reimbursements

rr_NetExpensesOverAssets

1.35%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

705

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

986

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,288

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,144

Annual Return 2002

rr_AnnualReturn2002

(16.46%)

Annual Return 2003

rr_AnnualReturn2003

46.94%

Annual Return 2004

rr_AnnualReturn2004

28.91%

Annual Return 2005

rr_AnnualReturn2005

21.42%

Annual Return 2006

rr_AnnualReturn2006

34.16%

Annual Return 2007

rr_AnnualReturn2007

16.90%

Annual Return 2008

rr_AnnualReturn2008

(46.09%)

Annual Return 2009

rr_AnnualReturn2009

50.40%

Annual Return 2010

rr_AnnualReturn2010

22.23%

Annual Return 2011

rr_AnnualReturn2011

(14.37%)

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-date return as of March 31, 2012: 14.99%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

14.99%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

2nd quarter 2009:

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

33.20%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

3rd quarter 2008:

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(23.79%)

1 Year

rr_AverageAnnualReturnYear01

(19.29%)

5 Years

rr_AverageAnnualReturnYear05

(1.33%)

10 Years

rr_AverageAnnualReturnYear10

9.20%

(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | Class A Shares | returns after taxes on distributions

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(19.82%)

5 Years

rr_AverageAnnualReturnYear05

(1.79%)

10 Years

rr_AverageAnnualReturnYear10

8.73%

(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | Class A Shares | returns after taxes on distributions and sale of Fund shares

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(12.29%)

5 Years

rr_AverageAnnualReturnYear05

(1.09%)

10 Years

rr_AverageAnnualReturnYear10

8.23%

(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | Class C Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[2]

Management fees

rr_ManagementFeesOverAssets

0.76%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other expenses

rr_OtherExpensesOverAssets

0.40%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

2.16%

Fee waivers and/or reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.02%)

^[7]

Total annual Fund operating expenses after fee waivers and/or reimbursements

rr_NetExpensesOverAssets

2.14%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

317

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

674

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,158

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,491

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

217

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

674

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

1,158

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

2,491

1 Year

rr_AverageAnnualReturnYear01

(15.85%)

5 Years

rr_AverageAnnualReturnYear05

(0.93%)

10 Years

rr_AverageAnnualReturnYear10

9.03%

(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | Class I Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

Management fees

rr_ManagementFeesOverAssets

0.76%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.10%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

0.86%

Fee waivers and/or reimbursements

rr_FeeWaiverOrReimbursementOverAssets

none

Total annual Fund operating expenses after fee waivers and/or reimbursements

rr_NetExpensesOverAssets

0.86%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

88

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

274

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

477

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,061

1 Year

rr_AverageAnnualReturnYear01

(14.02%)

5 Years

rr_AverageAnnualReturnYear05

0.22%

10 Years

rr_AverageAnnualReturnYear10

10.28%

(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | Class R Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

Management fees

rr_ManagementFeesOverAssets

0.76%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.50%

Other expenses

rr_OtherExpensesOverAssets

0.16%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.42%

Fee waivers and/or reimbursements

rr_FeeWaiverOrReimbursementOverAssets

none

Total annual Fund operating expenses after fee waivers and/or reimbursements

rr_NetExpensesOverAssets

1.42%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

145

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

449

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

776

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,702

1 Year

rr_AverageAnnualReturnYear01

(14.60%)

5 Years

rr_AverageAnnualReturnYear05

(0.42%)

10 Years

rr_AverageAnnualReturnYear10

9.58%

(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | Class R5 Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

Management fees

rr_ManagementFeesOverAssets

0.76%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.11%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

0.87%

Fee waivers and/or reimbursements

rr_FeeWaiverOrReimbursementOverAssets

none

Total annual Fund operating expenses after fee waivers and/or reimbursements

rr_NetExpensesOverAssets

0.87%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

89

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

278

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

482

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,073

1 Year

rr_AverageAnnualReturnYear01

(14.07%)

5 Years

rr_AverageAnnualReturnYear05

0.19%

10 Years

rr_AverageAnnualReturnYear10

10.26%

(Columbia Acorn International B) | (Columbia Acorn International)

Risk/Return:

rr_RiskReturnAbstract

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation.

Expense [Heading]

rr_ExpenseHeading

Fees and Expenses of the Fund

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

2013-08-14

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 32% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

32.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class B shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example Closing [Text Block]

rr_ExpenseExampleClosingTextBlock

Remember this is an example only. Your actual costs may be higher or lower.

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 75% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Brazil).

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Risk [Heading]

rr_RiskHeading

Principal Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Performance Information

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart below shows you how the performance of the Fund's Class B shares has varied from year to year.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800.345.6611

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.columbiamanagement.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Year by Year Total Return (%) as of December 31 Each Year

^[18]

Bar Chart Narrative [Text Block]

rr_BarChartNarrativeTextBlock

The bar chart below shows you how the performance of the Fund's Class B shares has varied from year to year.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    32.92%

Worst:   3rd quarter 2008:   -23.87%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Return as of December 31, 2011

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

The table compares the Fund's returns, for each period, with those of the Standard & Poor's (S&P) Global Ex-U.S. Between $500 Million and $5 Billion® Index, the Fund's primary benchmark, the S&P Global Ex-U.S. SmallCap® Index and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Global Ex-U.S. Between $500 Million and $5 Billion® Index is a subset of the broad market selected by the index sponsor that represents the mid- and small-cap developed and emerging markets, excluding the United States. The S&P Global Ex-U.S. SmallCap® Index is an unmanaged index consisting of the bottom 20% of institutionally investable capital of developed and emerging countries, excluding the United States. The performance of the S&P Global Ex-U.S. Small Cap® Index is provided to show how the Fund's performance compares to foreign market performance with a similar geographic distribution and wider market cap range than the Fund's primary benchmark. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund's performance compares to a widely recognized broad based index of foreign market performance.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn International B) | (Columbia Acorn International) | S&P Global Ex-U.S. Between $500 Million and $5 Billion® Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(16.94%)

5 Years

rr_AverageAnnualReturnYear05

(0.58%)

10 Years

rr_AverageAnnualReturnYear10

11.10%

(Columbia Acorn International B) | (Columbia Acorn International) | S&P Global Ex-U.S. SmallCap® Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(17.40%)

5 Years

rr_AverageAnnualReturnYear05

(2.14%)

10 Years

rr_AverageAnnualReturnYear10

10.33%

(Columbia Acorn International B) | (Columbia Acorn International) | MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(12.14%)

5 Years

rr_AverageAnnualReturnYear05

(4.72%)

10 Years

rr_AverageAnnualReturnYear10

4.67%

(Columbia Acorn International B) | (Columbia Acorn International) | Class B Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

5.00%

^[3]

Management fees

rr_ManagementFeesOverAssets

0.76%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.75%

Other expenses

rr_OtherExpensesOverAssets

0.60%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

2.11%

Fee waivers and/or reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.03%)

^[8]

Total annual Fund operating expenses after fee waivers and/or reimbursements

rr_NetExpensesOverAssets

2.08%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

711

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

958

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,331

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,255

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

211

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

658

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

1,131

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

2,255

Annual Return 2002

rr_AnnualReturn2002

(17.07%)

Annual Return 2003

rr_AnnualReturn2003

46.06%

Annual Return 2004

rr_AnnualReturn2004

27.91%

Annual Return 2005

rr_AnnualReturn2005

20.57%

Annual Return 2006

rr_AnnualReturn2006

33.26%

Annual Return 2007

rr_AnnualReturn2007

16.25%

Annual Return 2008

rr_AnnualReturn2008

(46.41%)

Annual Return 2009

rr_AnnualReturn2009

49.36%

Annual Return 2010

rr_AnnualReturn2010

21.49%

Annual Return 2011

rr_AnnualReturn2011

(14.92%)

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-date return as of March 31, 2012: 14.77%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

14.77%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

2nd quarter 2009:

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

32.92%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

3rd quarter 2008:

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(23.87%)

1 Year

rr_AverageAnnualReturnYear01

(19.07%)

5 Years

rr_AverageAnnualReturnYear05

(1.13%)

10 Years

rr_AverageAnnualReturnYear10

9.12%

(Columbia Acorn International B) | (Columbia Acorn International) | Class B Shares | returns after taxes on distributions

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(19.63%)

5 Years

rr_AverageAnnualReturnYear05

(1.53%)

10 Years

rr_AverageAnnualReturnYear10

8.74%

(Columbia Acorn International B) | (Columbia Acorn International) | Class B Shares | returns after taxes on distributions and sale of Fund shares

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(12.13%)

5 Years

rr_AverageAnnualReturnYear05

(0.90%)

10 Years

rr_AverageAnnualReturnYear10

8.20%

(Columbia Acorn International Z) | (Columbia Acorn International)

Risk/Return:

rr_RiskReturnAbstract

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation.

Expense [Heading]

rr_ExpenseHeading

Fees and Expenses of the Fund

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 32% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

32.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class Z shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example Closing [Text Block]

rr_ExpenseExampleClosingTextBlock

Remember this is an example only. Your actual costs may be higher or lower.

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 75% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Brazil).

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Risk [Heading]

rr_RiskHeading

Principal Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Performance Information

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart below shows you how the performance of the Fund's Class Z shares has varied from year to year.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800.345.6611

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.columbiamanagement.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Year by Year Total Return (%) as of December 31 Each Year

^[19]

Bar Chart Narrative [Text Block]

rr_BarChartNarrativeTextBlock

The bar chart below shows you how the performance of the Fund's Class Z shares has varied from year to year.

Bar Chart Does Not Reflect Sales Loads [Text]

rr_BarChartDoesNotReflectSalesLoads

These returns do not reflect deductions of sales charges, if any, paid by investors and would be lower if they did.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    33.30%

Worst:   3rd quarter 2008:   -23.68%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Return as of December 31, 2011

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

The table compares the Fund's returns, for each period, with those of the Standard & Poor's (S&P) Global Ex-U.S. Between $500 Million and $5 Billion® Index, the Fund's primary benchmark, the S&P Global Ex-U.S. SmallCap® Index and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Global Ex-U.S. Between $500 Million and $5 Billion® Index is a subset of the broad market selected by the index sponsor that represents the mid- and small-cap developed and emerging markets, excluding the United States. The S&P Global Ex-U.S. SmallCap® Index is an unmanaged index consisting of the bottom 20% of institutionally investable capital of developed and emerging countries, excluding the United States. The performance of the S&P Global Ex-U.S. Small Cap® Index is provided to show how the Fund's performance compares to foreign market performance with a similar geographic distribution and wider market cap range than the Fund's primary benchmark. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund's performance compares to a widely recognized broad based index of foreign market performance.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn International Z) | (Columbia Acorn International) | S&P Global Ex-U.S. Between $500 Million and $5 Billion® Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(16.94%)

5 Years

rr_AverageAnnualReturnYear05

(0.58%)

10 Years

rr_AverageAnnualReturnYear10

11.10%

(Columbia Acorn International Z) | (Columbia Acorn International) | S&P Global Ex-U.S. SmallCap® Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(17.40%)

5 Years

rr_AverageAnnualReturnYear05

(2.14%)

10 Years

rr_AverageAnnualReturnYear10

10.33%

(Columbia Acorn International Z) | (Columbia Acorn International) | MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(12.14%)

5 Years

rr_AverageAnnualReturnYear05

(4.72%)

10 Years

rr_AverageAnnualReturnYear10

4.67%

(Columbia Acorn International Z) | (Columbia Acorn International) | Class Z Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

none

Management fees

rr_ManagementFeesOverAssets

0.76%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.22%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

0.98%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

100

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

312

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

542

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,201

Annual Return 2002

rr_AnnualReturn2002

(16.10%)

Annual Return 2003

rr_AnnualReturn2003

47.80%

Annual Return 2004

rr_AnnualReturn2004

29.47%

Annual Return 2005

rr_AnnualReturn2005

21.81%

Annual Return 2006

rr_AnnualReturn2006

34.53%

Annual Return 2007

rr_AnnualReturn2007

17.28%

Annual Return 2008

rr_AnnualReturn2008

(45.89%)

Annual Return 2009

rr_AnnualReturn2009

50.97%

Annual Return 2010

rr_AnnualReturn2010

22.70%

Annual Return 2011

rr_AnnualReturn2011

(14.06%)

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-date return as of March 31, 2012: 15.07%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

15.07%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

2nd quarter 2009:

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

33.30%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

3rd quarter 2008:

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(23.68%)

1 Year

rr_AverageAnnualReturnYear01

(14.06%)

5 Years

rr_AverageAnnualReturnYear05

0.20%

10 Years

rr_AverageAnnualReturnYear10

10.27%

(Columbia Acorn International Z) | (Columbia Acorn International) | Class Z Shares | returns after taxes on distributions

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(14.63%)

5 Years

rr_AverageAnnualReturnYear05

(0.32%)

10 Years

rr_AverageAnnualReturnYear10

9.71%

(Columbia Acorn International Z) | (Columbia Acorn International) | Class Z Shares | returns after taxes on distributions and sale of Fund shares

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(8.88%)

5 Years

rr_AverageAnnualReturnYear05

0.20%

10 Years

rr_AverageAnnualReturnYear10

9.18%

(Columbia Acorn USA A,C & I) | (Columbia Acorn USA)

Risk/Return:

rr_RiskReturnAbstract

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation.

Expense [Heading]

rr_ExpenseHeading

Fees and Expenses of the Fund

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds. More information about these and other discounts is available from your financial advisor, in the Choosing a Share Class section beginning on page 17 of this prospectus and in Appendix D to the Statement of Additional Information under Sales Charge Waivers beginning on page D-1.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 20% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

20.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class A, Class C or Class I shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example Closing [Text Block]

rr_ExpenseExampleClosingTextBlock

Remember this is an example only. Your actual costs may be higher or lower.

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 80% of its net assets (plus any borrowings for investment purposes) in U.S. companies.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Risk [Heading]

rr_RiskHeading

Principal Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Performance Information

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The inception date for the Fund's Class I shares is September 27, 2010. The returns shown for Class I shares include the returns of the Fund's Class Z shares for periods prior to the inception date of Class I shares. Except for differences in expenses, Class I shares have annual returns substantially similar to those of Class Z shares, which are not offered in this prospectus, because all classes of the Fund's shares invest in the same portfolio of securities.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart below shows you how the performance of the Fund's Class A shares has varied from year to year.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800.345.6611

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.columbiamanagement.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Year by Year Total Return (%) as of December 31 Each Year

^[20]

Bar Chart Narrative [Text Block]

rr_BarChartNarrativeTextBlock

The bar chart below shows you how the performance of the Fund's Class A shares has varied from year to year. These returns do not reflect deductions of sales charges, if any, paid by investors and would be lower if they did.

Bar Chart Does Not Reflect Sales Loads [Text]

rr_BarChartDoesNotReflectSalesLoads

These returns do not reflect deductions of sales charges, if any, paid by investors and would be lower if they did.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best and Worst Quarterly Returns During this Period

Best:    3rd quarter 2009:    23.37%

Worst:   4th quarter 2008:   -27.99%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Return as of December 31, 2011

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

The after-tax returns are shown only for Class A shares and will vary for other share classes.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

The table compares the Fund's returns for each period with those of the Russell 2000 Index. This index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown only for Class A shares and will vary for other share classes.

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn USA A,C & I) | (Columbia Acorn USA) | Russell 2000 Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(4.18%)

5 Years

rr_AverageAnnualReturnYear05

0.15%

10 Years

rr_AverageAnnualReturnYear10

5.62%

(Columbia Acorn USA A,C & I) | (Columbia Acorn USA) | Class A Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[1]

Management fees

rr_ManagementFeesOverAssets

0.86%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.22%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.33%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

703

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

972

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,262

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,084

Annual Return 2002

rr_AnnualReturn2002

(18.97%)

Annual Return 2003

rr_AnnualReturn2003

46.26%

Annual Return 2004

rr_AnnualReturn2004

20.12%

Annual Return 2005

rr_AnnualReturn2005

12.68%

Annual Return 2006

rr_AnnualReturn2006

7.95%

Annual Return 2007

rr_AnnualReturn2007

3.18%

Annual Return 2008

rr_AnnualReturn2008

(39.38%)

Annual Return 2009

rr_AnnualReturn2009

41.07%

Annual Return 2010

rr_AnnualReturn2010

22.78%

Annual Return 2011

rr_AnnualReturn2011

(5.21%)

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-date return as of March 31, 2012: 16.27%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

16.27%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

3rd quarter 2009:

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

23.37%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

4th quarter 2008:

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(27.99%)

1 Year

rr_AverageAnnualReturnYear01

(10.66%)

5 Years

rr_AverageAnnualReturnYear05

(0.65%)

10 Years

rr_AverageAnnualReturnYear10

5.30%

(Columbia Acorn USA A,C & I) | (Columbia Acorn USA) | Class A Shares | returns after taxes on distributions

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(10.74%)

5 Years

rr_AverageAnnualReturnYear05

(0.95%)

10 Years

rr_AverageAnnualReturnYear10

5.02%

(Columbia Acorn USA A,C & I) | (Columbia Acorn USA) | Class A Shares | returns after taxes on distributions and sale of Fund shares

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(6.81%)

5 Years

rr_AverageAnnualReturnYear05

(0.55%)

10 Years

rr_AverageAnnualReturnYear10

4.63%

(Columbia Acorn USA A,C & I) | (Columbia Acorn USA) | Class C Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[2]

Management fees

rr_ManagementFeesOverAssets

0.86%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other expenses

rr_OtherExpensesOverAssets

0.32%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

2.18%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

321

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

682

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,169

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,513

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

221

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

682

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

1,169

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

2,513

1 Year

rr_AverageAnnualReturnYear01

(6.86%)

5 Years

rr_AverageAnnualReturnYear05

(0.25%)

10 Years

rr_AverageAnnualReturnYear10

5.14%

(Columbia Acorn USA A,C & I) | (Columbia Acorn USA) | Class I Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

Management fees

rr_ManagementFeesOverAssets

0.86%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.09%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

0.95%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

97

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

303

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

525

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,166

1 Year

rr_AverageAnnualReturnYear01

(4.88%)

5 Years

rr_AverageAnnualReturnYear05

0.83%

10 Years

rr_AverageAnnualReturnYear10

6.31%

(Columbia Acorn USA B) | (Columbia Acorn USA)

Risk/Return:

rr_RiskReturnAbstract

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation.

Expense [Heading]

rr_ExpenseHeading

Fees and Expenses of the Fund

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 20% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

20.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class B shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example Closing [Text Block]

rr_ExpenseExampleClosingTextBlock

Remember this is an example only. Your actual costs may be higher or lower.

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 80% of its net assets (plus any borrowings for investment purposes) in U.S. companies.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Risk [Heading]

rr_RiskHeading

Principal Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Performance Information

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart below shows you how the performance of the Fund's Class B shares has varied from year to year.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800.345.6611

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.columbiamanagement.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Year by Year Total Return (%) as of December 31 Each Year

^[21]

Bar Chart Narrative [Text Block]

rr_BarChartNarrativeTextBlock

The bar chart below shows you how the performance of the Fund's Class B shares has varied from year to year.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best and Worst Quarterly Returns During this Period

Best:    3rd quarter 2009:    23.15%

Worst:   4th quarter 2008:   -28.08%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Return as of December 31, 2011

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

The table compares the Fund's returns for each period with those of the Russell 2000 Index. This index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn USA B) | (Columbia Acorn USA) | Russell 2000 Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(4.18%)

5 Years

rr_AverageAnnualReturnYear05

0.15%

10 Years

rr_AverageAnnualReturnYear10

5.62%

(Columbia Acorn USA B) | (Columbia Acorn USA) | Class B Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

5.00%

^[3]

Management fees

rr_ManagementFeesOverAssets

0.86%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.75%

Other expenses

rr_OtherExpensesOverAssets

0.49%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

2.10%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

713

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

958

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,329

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,234

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

213

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

658

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

1,129

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

2,234

Annual Return 2002

rr_AnnualReturn2002

(19.48%)

Annual Return 2003

rr_AnnualReturn2003

45.32%

Annual Return 2004

rr_AnnualReturn2004

19.26%

Annual Return 2005

rr_AnnualReturn2005

11.84%

Annual Return 2006

rr_AnnualReturn2006

7.29%

Annual Return 2007

rr_AnnualReturn2007

2.53%

Annual Return 2008

rr_AnnualReturn2008

(39.75%)

Annual Return 2009

rr_AnnualReturn2009

40.12%

Annual Return 2010

rr_AnnualReturn2010

21.96%

Annual Return 2011

rr_AnnualReturn2011

(5.68%)

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-date return as of March 31, 2012: 16.06%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

16.06%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

3rd quarter 2009:

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

23.15%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

4th quarter 2008:

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(28.08%)

1 Year

rr_AverageAnnualReturnYear01

(10.36%)

5 Years

rr_AverageAnnualReturnYear05

(0.45%)

10 Years

rr_AverageAnnualReturnYear10

5.25%

(Columbia Acorn USA B) | (Columbia Acorn USA) | Class B Shares | returns after taxes on distributions

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(10.46%)

5 Years

rr_AverageAnnualReturnYear05

(0.77%)

10 Years

rr_AverageAnnualReturnYear10

4.95%

(Columbia Acorn USA B) | (Columbia Acorn USA) | Class B Shares | returns after taxes on distributions and sale of Fund shares

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(6.60%)

5 Years

rr_AverageAnnualReturnYear05

(0.37%)

10 Years

rr_AverageAnnualReturnYear10

4.59%

(Columbia Acorn USA Z) | (Columbia Acorn USA)

Risk/Return:

rr_RiskReturnAbstract

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation.

Expense [Heading]

rr_ExpenseHeading

Fees and Expenses of the Fund

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 20% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

20.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class Z shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example Closing [Text Block]

rr_ExpenseExampleClosingTextBlock

Remember this is an example only. Your actual costs may be higher or lower.

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 80% of its net assets (plus any borrowings for investment purposes) in U.S. companies.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Risk [Heading]

rr_RiskHeading

Principal Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Performance Information

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart below shows you how the performance of the Fund's Class Z shares has varied from year to year.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800.345.6611

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.columbiamanagement.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Year by Year Total Return (%) as of December 31 Each Year

^[22]

Bar Chart Narrative [Text Block]

rr_BarChartNarrativeTextBlock

The bar chart below shows you how the performance of the Fund's Class Z shares has varied from year to year.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best and Worst Quarterly Returns During this Period

Best:    3rd quarter 2009:    23.55%

Worst:   4th quarter 2008:   -27.96%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Return as of December 31, 2011

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

The table compares the Fund's returns for each period with those of the Russell 2000 Index. This index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn USA Z) | (Columbia Acorn USA) | Russell 2000 Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(4.18%)

5 Years

rr_AverageAnnualReturnYear05

0.15%

10 Years

rr_AverageAnnualReturnYear10

5.62%

(Columbia Acorn USA Z) | (Columbia Acorn USA) | Class Z Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

none

Management fees

rr_ManagementFeesOverAssets

0.86%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.19%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.05%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

107

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

334

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

579

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,283

Annual Return 2002

rr_AnnualReturn2002

(18.49%)

Annual Return 2003

rr_AnnualReturn2003

47.13%

Annual Return 2004

rr_AnnualReturn2004

20.62%

Annual Return 2005

rr_AnnualReturn2005

12.98%

Annual Return 2006

rr_AnnualReturn2006

8.28%

Annual Return 2007

rr_AnnualReturn2007

3.46%

Annual Return 2008

rr_AnnualReturn2008

(39.22%)

Annual Return 2009

rr_AnnualReturn2009

41.49%

Annual Return 2010

rr_AnnualReturn2010

23.16%

Annual Return 2011

rr_AnnualReturn2011

(4.95%)

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-date return as of March 31, 2012: 16.38%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

16.38%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

3rd quarter 2009:

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

23.55%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

4th quarter 2008:

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(27.96%)

1 Year

rr_AverageAnnualReturnYear01

(4.95%)

5 Years

rr_AverageAnnualReturnYear05

0.82%

10 Years

rr_AverageAnnualReturnYear10

6.30%

(Columbia Acorn USA Z) | (Columbia Acorn USA) | Class Z Shares | returns after taxes on distributions

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(5.04%)

5 Years

rr_AverageAnnualReturnYear05

0.52%

10 Years

rr_AverageAnnualReturnYear10

6.02%

(Columbia Acorn USA Z) | (Columbia Acorn USA) | Class Z Shares | returns after taxes on distributions and sale of Fund shares

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(3.10%)

5 Years

rr_AverageAnnualReturnYear05

0.69%

10 Years

rr_AverageAnnualReturnYear10

5.54%

(Columbia Acorn Select A,C & I) | (Columbia Acorn Select)

Risk/Return:

rr_RiskReturnAbstract

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation.

Expense [Heading]

rr_ExpenseHeading

Fees and Expenses of the Fund

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds. More information about these and other discounts is available from your financial advisor, in the Choosing a Share Class section beginning on page 18 of this prospectus and in Appendix D to the Statement of Additional Information under Sales Charge Waivers beginning on page D-1.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 21% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

21.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class A, Class C or Class I shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example Closing [Text Block]

rr_ExpenseExampleClosingTextBlock

Remember this is an example only. Your actual costs may be higher or lower.

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of companies with market capitalizations under $20 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $20 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $20 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $20 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $20 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Colombia).

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Fund may also invest in companies that the Investment Manager believes have good operational fundamentals but that the Investment Manager believes are undervalued due to negative investor sentiment related to company-specific or market-related conditions. Investments in turnaround and development stage companies may also be made when the Investment Manager believes potential returns outweigh risks of losses.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Risk [Heading]

rr_RiskHeading

Principal Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Opportunistic Investing Risk - Undervalued securities involve the risk that they may never reach their expected full market value, either because the market fails to recognize the security's intrinsic worth or the expected value was misgauged. Undervalued securities also may decline in price even though the Investment Manager believes they are already undervalued. Turnaround companies may never improve their fundamentals, may take much longer than expected to improve, or may improve much less than expected. Development stage companies could fail to develop and deplete their assets, resulting in large percentage losses.

Bar Chart and Performance Table [Heading]

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Performance Information

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The inception date for the Fund's Class I shares is September 27, 2010. The returns shown for Class I shares include the returns of the Fund's Class Z shares for periods prior to the inception date of Class I shares. Except for differences in expenses, Class I shares have annual returns substantially similar to those of Class Z shares, which are not offered in this prospectus, because all classes of the Fund's shares invest in the same portfolio of securities.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart below shows you how the performance of the Fund's Class A shares has varied from year to year.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800.345.6611

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.columbiamanagement.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Year by Year Total Return (%) as of December 31 Each Year

^[23]

Bar Chart Narrative [Text Block]

rr_BarChartNarrativeTextBlock

The bar chart below shows you how the performance of the Fund's Class A shares has varied from year to year. These returns do not reflect deductions of sales charges, if any, paid by investors and would be lower if they did.

Bar Chart Does Not Reflect Sales Loads [Text]

rr_BarChartDoesNotReflectSalesLoads

These returns do not reflect deductions of sales charges, if any, paid by investors and would be lower if they did.

Bar Chart Closing [Text Block]

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Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    28.01%

Worst:   4th quarter 2008:   -30.17%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Return as of December 31, 2011

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

The after-tax returns are shown only for Class A shares and will vary for other share classes.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

The table compares the Fund's returns for each period with those of the Standard & Poor's (S&P) MidCap 400® Index, the Fund's primary benchmark, and the S&P 500® Index. The S&P MidCap 400® Index is a market value-weighted index that tracks the performance of 400 mid-cap U.S. companies. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in companies with market capitalizations under $20 billion at the time of investment, the comparison to the S&P 500® Index is presented to show performance against a widely recognized market index.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown only for Class A shares and will vary for other share classes.

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn Select A,C & I) | (Columbia Acorn Select) | S&P MidCap 400® Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(1.73%)

5 Years

rr_AverageAnnualReturnYear05

3.32%

10 Years

rr_AverageAnnualReturnYear10

7.04%

(Columbia Acorn Select A,C & I) | (Columbia Acorn Select) | S&P 500® Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

2.11%

5 Years

rr_AverageAnnualReturnYear05

(0.25%)

10 Years

rr_AverageAnnualReturnYear10

2.92%

(Columbia Acorn Select A,C & I) | (Columbia Acorn Select) | Class A Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[1]

Management fees

rr_ManagementFeesOverAssets

0.82%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.28%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.35%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

705

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

978

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,272

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,105

Annual Return 2002

rr_AnnualReturn2002

(8.17%)

Annual Return 2003

rr_AnnualReturn2003

29.95%

Annual Return 2004

rr_AnnualReturn2004

18.16%

Annual Return 2005

rr_AnnualReturn2005

10.78%

Annual Return 2006

rr_AnnualReturn2006

19.32%

Annual Return 2007

rr_AnnualReturn2007

8.92%

Annual Return 2008

rr_AnnualReturn2008

(49.31%)

Annual Return 2009

rr_AnnualReturn2009

65.65%

Annual Return 2010

rr_AnnualReturn2010

22.49%

Annual Return 2011

rr_AnnualReturn2011

(16.65%)

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-date return as of March 31, 2012: 17.65%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

17.65%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

2nd quarter 2009:

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

28.01%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

4th quarter 2008:

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(30.17%)

1 Year

rr_AverageAnnualReturnYear01

(21.43%)

5 Years

rr_AverageAnnualReturnYear05

(2.52%)

10 Years

rr_AverageAnnualReturnYear10

5.07%

(Columbia Acorn Select A,C & I) | (Columbia Acorn Select) | Class A Shares | returns after taxes on distributions

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(21.83%)

5 Years

rr_AverageAnnualReturnYear05

(2.76%)

10 Years

rr_AverageAnnualReturnYear10

4.82%

(Columbia Acorn Select A,C & I) | (Columbia Acorn Select) | Class A Shares | returns after taxes on distributions and sale of Fund shares

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(13.89%)

5 Years

rr_AverageAnnualReturnYear05

(2.16%)

10 Years

rr_AverageAnnualReturnYear10

4.40%

(Columbia Acorn Select A,C & I) | (Columbia Acorn Select) | Class C Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[2]

Management fees

rr_ManagementFeesOverAssets

0.82%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other expenses

rr_OtherExpensesOverAssets

0.35%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

2.17%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

320

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

679

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,164

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,503

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

220

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

679

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

1,164

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

2,503

1 Year

rr_AverageAnnualReturnYear01

(18.09%)

5 Years

rr_AverageAnnualReturnYear05

(2.15%)

10 Years

rr_AverageAnnualReturnYear10

4.89%

(Columbia Acorn Select A,C & I) | (Columbia Acorn Select) | Class I Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

Management fees

rr_ManagementFeesOverAssets

0.82%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.09%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

0.91%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

93

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

290

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

504

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,120

1 Year

rr_AverageAnnualReturnYear01

(16.25%)

5 Years

rr_AverageAnnualReturnYear05

(1.03%)

10 Years

rr_AverageAnnualReturnYear10

6.07%

(Columbia Acorn Select B) | (Columbia Acorn Select)

Risk/Return:

rr_RiskReturnAbstract

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation.

Expense [Heading]

rr_ExpenseHeading

Fees and Expenses of the Fund

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 21% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

21.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class B shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example Closing [Text Block]

rr_ExpenseExampleClosingTextBlock

Remember this is an example only. Your actual costs may be higher or lower.

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of companies with market capitalizations under $20 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $20 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $20 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $20 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $20 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Colombia).

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Fund may also invest in companies that the Investment Manager believes have good operational fundamentals but that the Investment Manager believes are undervalued due to negative investor sentiment related to company-specific or market-related conditions. Investments in turnaround and development stage companies may also be made when the Investment Manager believes potential returns outweigh risks of losses.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Risk [Heading]

rr_RiskHeading

Principal Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Opportunistic Investing Risk - Undervalued securities involve the risk that they may never reach their expected full market value, either because the market fails to recognize the security's intrinsic worth or the expected value was misgauged. Undervalued securities also may decline in price even though the Investment Manager believes they are already undervalued. Turnaround companies may never improve their fundamentals, may take much longer than expected to improve, or may improve much less than expected. Development stage companies could fail to develop and deplete their assets, resulting in large percentage losses.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Performance Information

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart below shows you how the performance of the Fund's Class B shares has varied from year to year.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800.345.6611

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.columbiamanagement.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Year by Year Total Return (%) as of December 31 Each Year

^[24]

Bar Chart Narrative [Text Block]

rr_BarChartNarrativeTextBlock

The bar chart below shows you how the performance of the Fund's Class B shares has varied from year to year.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    27.78%

Worst:   4th quarter 2008:   -30.26%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Return as of December 31, 2011

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

The table compares the Fund's returns for each period with those of the Standard & Poor's (S&P) MidCap 400® Index, the Fund's primary benchmark, and the S&P 500® Index. The S&P MidCap 400® Index is a market value-weighted index that tracks the performance of 400 mid-cap U.S. companies. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in companies with market capitalizations under $20 billion at the time of investment, the comparison to the S&P 500® Index is presented to show performance against a widely recognized market index.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn Select B) | (Columbia Acorn Select) | S&P MidCap 400® Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(1.73%)

5 Years

rr_AverageAnnualReturnYear05

3.32%

10 Years

rr_AverageAnnualReturnYear10

7.04%

(Columbia Acorn Select B) | (Columbia Acorn Select) | S&P 500® Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

2.11%

5 Years

rr_AverageAnnualReturnYear05

(0.25%)

10 Years

rr_AverageAnnualReturnYear10

2.92%

(Columbia Acorn Select B) | (Columbia Acorn Select) | Class B Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

5.00%

^[3]

Management fees

rr_ManagementFeesOverAssets

0.82%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.75%

Other expenses

rr_OtherExpensesOverAssets

0.48%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

2.05%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

708

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

943

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,303

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,200

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

208

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

643

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

1,103

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

2,200

Annual Return 2002

rr_AnnualReturn2002

(8.77%)

Annual Return 2003

rr_AnnualReturn2003

29.14%

Annual Return 2004

rr_AnnualReturn2004

17.24%

Annual Return 2005

rr_AnnualReturn2005

10.01%

Annual Return 2006

rr_AnnualReturn2006

18.54%

Annual Return 2007

rr_AnnualReturn2007

8.22%

Annual Return 2008

rr_AnnualReturn2008

(49.62%)

Annual Return 2009

rr_AnnualReturn2009

64.44%

Annual Return 2010

rr_AnnualReturn2010

21.72%

Annual Return 2011

rr_AnnualReturn2011

(17.11%)

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-date return as of March 31, 2012: 17.48%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

17.48%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

2nd quarter 2009:

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

27.78%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

4th quarter 2008:

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(30.26%)

1 Year

rr_AverageAnnualReturnYear01

(21.22%)

5 Years

rr_AverageAnnualReturnYear05

(2.36%)

10 Years

rr_AverageAnnualReturnYear10

5.00%

(Columbia Acorn Select B) | (Columbia Acorn Select) | Class B Shares | returns after taxes on distributions

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(21.49%)

5 Years

rr_AverageAnnualReturnYear05

(2.58%)

10 Years

rr_AverageAnnualReturnYear10

4.77%

(Columbia Acorn Select B) | (Columbia Acorn Select) | Class B Shares | returns after taxes on distributions and sale of Fund shares

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(13.77%)

5 Years

rr_AverageAnnualReturnYear05

(2.00%)

10 Years

rr_AverageAnnualReturnYear10

4.36%

(Columbia Acorn Select Z) | (Columbia Acorn Select)

Risk/Return:

rr_RiskReturnAbstract

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation.

Expense [Heading]

rr_ExpenseHeading

Fees and Expenses of the Fund

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 21% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

21.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class Z shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example Closing [Text Block]

rr_ExpenseExampleClosingTextBlock

Remember this is an example only. Your actual costs may be higher or lower.

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of companies with market capitalizations under $20 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $20 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $20 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $20 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $20 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Colombia).

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Fund may also invest in companies that the Investment Manager believes have good operational fundamentals but that the Investment Manager believes are undervalued due to negative investor sentiment related to company-specific or market-related conditions. Investments in turnaround and development stage companies may also be made when the Investment Manager believes potential returns outweigh risks of losses.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Risk [Heading]

rr_RiskHeading

Principal Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Opportunistic Investing Risk - Undervalued securities involve the risk that they may never reach their expected full market value, either because the market fails to recognize the security's intrinsic worth or the expected value was misgauged. Undervalued securities also may decline in price even though the Investment Manager believes they are already undervalued. Turnaround companies may never improve their fundamentals, may take much longer than expected to improve, or may improve much less than expected. Development stage companies could fail to develop and deplete their assets, resulting in large percentage losses.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Performance Information

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart below shows you how the performance of the Fund's Class Z shares has varied from year to year.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800.345.6611

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.columbiamanagement.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Year by Year Total Return (%) as of December 31 Each Year

^[25]

Bar Chart Narrative [Text Block]

rr_BarChartNarrativeTextBlock

The bar chart below shows you how the performance of the Fund's Class Z shares has varied from year to year.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    28.11%

Worst:   4th quarter 2008:   -30.14%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Return as of December 31, 2011

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

The table compares the Fund's returns for each period with those of the Standard & Poor's (S&P) MidCap 400® Index, the Fund's primary benchmark, and the S&P 500® Index. The S&P MidCap 400® Index is a market value-weighted index that tracks the performance of 400 mid-cap U.S. companies. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in companies with market capitalizations under $20 billion at the time of investment, the comparison to the S&P 500® Index is presented to show performance against a widely recognized market index.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn Select Z) | (Columbia Acorn Select) | S&P MidCap 400® Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(1.73%)

5 Years

rr_AverageAnnualReturnYear05

3.32%

10 Years

rr_AverageAnnualReturnYear10

7.04%

(Columbia Acorn Select Z) | (Columbia Acorn Select) | S&P 500® Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

2.11%

5 Years

rr_AverageAnnualReturnYear05

(0.25%)

10 Years

rr_AverageAnnualReturnYear10

2.92%

(Columbia Acorn Select Z) | (Columbia Acorn Select) | Class Z Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

none

Management fees

rr_ManagementFeesOverAssets

0.82%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.18%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.00%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

102

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

318

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

552

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,225

Annual Return 2002

rr_AnnualReturn2002

(7.81%)

Annual Return 2003

rr_AnnualReturn2003

30.61%

Annual Return 2004

rr_AnnualReturn2004

18.58%

Annual Return 2005

rr_AnnualReturn2005

11.08%

Annual Return 2006

rr_AnnualReturn2006

19.68%

Annual Return 2007

rr_AnnualReturn2007

9.20%

Annual Return 2008

rr_AnnualReturn2008

(49.18%)

Annual Return 2009

rr_AnnualReturn2009

66.17%

Annual Return 2010

rr_AnnualReturn2010

22.88%

Annual Return 2011

rr_AnnualReturn2011

(16.37%)

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-date return as of March 31, 2012: 17.70%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

17.70%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

2nd quarter 2009:

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

28.11%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

4th quarter 2008:

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(30.14%)

1 Year

rr_AverageAnnualReturnYear01

(16.37%)

5 Years

rr_AverageAnnualReturnYear05

(1.07%)

10 Years

rr_AverageAnnualReturnYear10

6.05%

(Columbia Acorn Select Z) | (Columbia Acorn Select) | Class Z Shares | returns after taxes on distributions

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(16.87%)

5 Years

rr_AverageAnnualReturnYear05

(1.33%)

10 Years

rr_AverageAnnualReturnYear10

5.77%

(Columbia Acorn Select Z) | (Columbia Acorn Select) | Class Z Shares | returns after taxes on distributions and sale of Fund shares

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(10.60%)

5 Years

rr_AverageAnnualReturnYear05

(0.95%)

10 Years

rr_AverageAnnualReturnYear10

5.27%

(Columbia Acorn International Select A,C & I) | (Columbia Acorn International Select)

Risk/Return:

rr_RiskReturnAbstract

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation.

Expense [Heading]

rr_ExpenseHeading

Fees and Expenses of the Fund

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds. More information about these and other discounts is available from your financial advisor, in the Choosing a Share Class section beginning on page 18 of this prospectus and in Appendix D to the Statement of Additional Information under Sales Charge Waivers beginning on page D-1.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 44% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

44.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class A, Class C or Class I shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example Closing [Text Block]

rr_ExpenseExampleClosingTextBlock

Remember this is an example only. Your actual costs may be higher or lower.

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 65% of its net assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom). The Fund also may invest up to 35% of its total assets in companies in emerging markets (for example, China, India and Brazil). The Fund generally invests in at least three countries other than the United States but may invest up to 25% of its total assets in securities of U.S. issuers.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $25 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $25 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $25 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $25 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $25 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies. The Fund also may invest in larger-sized companies.

The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to invest in a limited number of foreign companies (generally between 40-60), offering the potential to provide above-average growth over time.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Risk [Heading]

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Principal Risks

Risk Narrative [Text Block]

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• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Bar Chart and Performance Table [Heading]

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Performance Information

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The inception date for the Fund's Class I shares is September 27, 2010. The returns shown for Class I shares include the returns of the Fund's Class Z shares for periods prior to the inception date of Class I shares. Except for differences in expenses, Class I shares have annual returns substantially similar to those of Class Z shares, which are not offered in this prospectus, because all classes of the Fund's shares invest in the same portfolio of securities.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart below shows you how the performance of the Fund's Class A shares has varied from year to year.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800.345.6611

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.columbiamanagement.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.

Bar Chart [Heading]

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Year by Year Total Return (%) as of December 31 Each Year

^[26]

Bar Chart Narrative [Text Block]

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The bar chart below shows you how the performance of the Fund's Class A shares has varied from year to year. These returns do not reflect deductions of sales charges, if any, paid by investors and would be lower if they did.

Bar Chart Does Not Reflect Sales Loads [Text]

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These returns do not reflect deductions of sales charges, if any, paid by investors and would be lower if they did.

Bar Chart Closing [Text Block]

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Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    23.32%

Worst:   3rd quarter 2008:   -24.85%

Performance Table Heading

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Average Annual Total Return as of December 31, 2011

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

The after-tax returns are shown only for Class A shares and will vary for other share classes.

Performance Table Explanation after Tax Higher

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Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

The table compares the Fund's returns, for each period, with those of the Standard & Poor's (S&P) Developed Ex-U.S. Between $2 Billion and $10 Billion® Index, the Fund's primary benchmark, and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index is a subset of the broad market selected by the index sponsor that represents the mid-cap developed market excluding the United States. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund's performance compares to a widely recognized broad based index of foreign market performance.

Performance Table Closing [Text Block]

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The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown only for Class A shares and will vary for other share classes.

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn International Select A,C & I) | (Columbia Acorn International Select) | S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(14.01%)

5 Years

rr_AverageAnnualReturnYear05

(3.06%)

10 Years

rr_AverageAnnualReturnYear10

8.41%

(Columbia Acorn International Select A,C & I) | (Columbia Acorn International Select) | MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(12.14%)

5 Years

rr_AverageAnnualReturnYear05

(4.72%)

10 Years

rr_AverageAnnualReturnYear10

4.67%

(Columbia Acorn International Select A,C & I) | (Columbia Acorn International Select) | Class A Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[1]

Management fees

rr_ManagementFeesOverAssets

0.94%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.43%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.62%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

730

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

1,057

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,406

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,386

Annual Return 2002

rr_AnnualReturn2002

(15.16%)

Annual Return 2003

rr_AnnualReturn2003

41.11%

Annual Return 2004

rr_AnnualReturn2004

23.76%

Annual Return 2005

rr_AnnualReturn2005

15.60%

Annual Return 2006

rr_AnnualReturn2006

35.97%

Annual Return 2007

rr_AnnualReturn2007

21.50%

Annual Return 2008

rr_AnnualReturn2008

(42.30%)

Annual Return 2009

rr_AnnualReturn2009

31.01%

Annual Return 2010

rr_AnnualReturn2010

21.41%

Annual Return 2011

rr_AnnualReturn2011

(10.11%)

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-date return as of March 31, 2012: 11.29%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

11.29%

Highest Quarterly Return, Label

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2nd quarter 2009:

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

23.32%

Lowest Quarterly Return, Label

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3rd quarter 2008:

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(24.85%)

1 Year

rr_AverageAnnualReturnYear01

(15.28%)

5 Years

rr_AverageAnnualReturnYear05

(1.13%)

10 Years

rr_AverageAnnualReturnYear10

8.20%

(Columbia Acorn International Select A,C & I) | (Columbia Acorn International Select) | Class A Shares | returns after taxes on distributions

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(15.64%)

5 Years

rr_AverageAnnualReturnYear05

(1.47%)

10 Years

rr_AverageAnnualReturnYear10

8.04%

(Columbia Acorn International Select A,C & I) | (Columbia Acorn International Select) | Class A Shares | returns after taxes on distributions and sale of Fund shares

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(9.14%)

5 Years

rr_AverageAnnualReturnYear05

(0.86%)

10 Years

rr_AverageAnnualReturnYear10

7.38%

(Columbia Acorn International Select A,C & I) | (Columbia Acorn International Select) | Class C Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[2]

Management fees

rr_ManagementFeesOverAssets

0.94%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other expenses

rr_OtherExpensesOverAssets

0.50%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

2.44%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

347

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

761

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,301

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,776

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

247

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

761

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

1,301

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

2,776

1 Year

rr_AverageAnnualReturnYear01

(11.69%)

5 Years

rr_AverageAnnualReturnYear05

(0.75%)

10 Years

rr_AverageAnnualReturnYear10

8.03%

(Columbia Acorn International Select A,C & I) | (Columbia Acorn International Select) | Class I Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

Management fees

rr_ManagementFeesOverAssets

0.94%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.14%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.08%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

110

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

343

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

595

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,317

1 Year

rr_AverageAnnualReturnYear01

(9.68%)

5 Years

rr_AverageAnnualReturnYear05

0.43%

10 Years

rr_AverageAnnualReturnYear10

9.24%

(Columbia Acorn International Select B) | (Columbia Acorn International Select)

Risk/Return:

rr_RiskReturnAbstract

Objective [Heading]

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Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation.

Expense [Heading]

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Fees and Expenses of the Fund

Expense Narrative [Text Block]

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This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

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The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 44% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

44.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class B shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example Closing [Text Block]

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Remember this is an example only. Your actual costs may be higher or lower.

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 65% of its net assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom). The Fund also may invest up to 35% of its total assets in companies in emerging markets (for example, China, India and Brazil). The Fund generally invests in at least three countries other than the United States but may invest up to 25% of its total assets in securities of U.S. issuers.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $25 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $25 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $25 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $25 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $25 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies. The Fund also may invest in larger-sized companies.

The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to invest in a limited number of foreign companies (generally between 40-60), offering the potential to provide above-average growth over time.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Risk [Heading]

rr_RiskHeading

Principal Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Performance Information

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart below shows you how the performance of the Fund's Class B shares has varied from year to year.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800.345.6611

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.columbiamanagement.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Year by Year Total Return (%) as of December 31 Each Year

^[27]

Bar Chart Narrative [Text Block]

rr_BarChartNarrativeTextBlock

The bar chart below shows you how the performance of the Fund's Class B shares has varied from year to year.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    23.09%

Worst:   3rd quarter 2008:   -24.96%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Return as of December 31, 2011

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

The table compares the Fund's returns, for each period, with those of the Standard & Poor's (S&P) Developed Ex-U.S. Between $2 Billion and $10 Billion® Index, the Fund's primary benchmark, and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index is a subset of the broad market selected by the index sponsor that represents the mid-cap developed market excluding the United States. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund's performance compares to a widely recognized broad based index of foreign market performance.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn International Select B) | (Columbia Acorn International Select) | S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(14.01%)

5 Years

rr_AverageAnnualReturnYear05

(3.06%)

10 Years

rr_AverageAnnualReturnYear10

8.41%

(Columbia Acorn International Select B) | (Columbia Acorn International Select) | MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(12.14%)

5 Years

rr_AverageAnnualReturnYear05

(4.72%)

10 Years

rr_AverageAnnualReturnYear10

4.67%

(Columbia Acorn International Select B) | (Columbia Acorn International Select) | Class B Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

5.00%

^[3]

Management fees

rr_ManagementFeesOverAssets

0.94%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.75%

Other expenses

rr_OtherExpensesOverAssets

0.63%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

2.32%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

735

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

1,024

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,440

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,481

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

235

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

724

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

1,240

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

2,481

Annual Return 2002

rr_AnnualReturn2002

(15.72%)

Annual Return 2003

rr_AnnualReturn2003

40.08%

Annual Return 2004

rr_AnnualReturn2004

22.95%

Annual Return 2005

rr_AnnualReturn2005

14.97%

Annual Return 2006

rr_AnnualReturn2006

35.00%

Annual Return 2007

rr_AnnualReturn2007

20.69%

Annual Return 2008

rr_AnnualReturn2008

(42.68%)

Annual Return 2009

rr_AnnualReturn2009

30.19%

Annual Return 2010

rr_AnnualReturn2010

20.63%

Annual Return 2011

rr_AnnualReturn2011

(10.64%)

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-date return as of March 31, 2012: 11.13%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

11.13%

1 Year

rr_AverageAnnualReturnYear01

(14.99%)

5 Years

rr_AverageAnnualReturnYear05

(0.95%)

10 Years

rr_AverageAnnualReturnYear10

8.14%

(Columbia Acorn International Select B) | (Columbia Acorn International Select) | Class B Shares | returns after taxes on distributions

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(15.22%)

5 Years

rr_AverageAnnualReturnYear05

(1.21%)

10 Years

rr_AverageAnnualReturnYear10

8.04%

(Columbia Acorn International Select B) | (Columbia Acorn International Select) | Class B Shares | returns after taxes on distributions and sale of Fund shares

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(9.13%)

5 Years

rr_AverageAnnualReturnYear05

(0.69%)

10 Years

rr_AverageAnnualReturnYear10

7.33%

(Columbia Acorn International Select Z) | (Columbia Acorn International Select)

Risk/Return:

rr_RiskReturnAbstract

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation.

Expense [Heading]

rr_ExpenseHeading

Fees and Expenses of the Fund

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 44% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

44.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class Z shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example Closing [Text Block]

rr_ExpenseExampleClosingTextBlock

Remember this is an example only. Your actual costs may be higher or lower.

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 65% of its net assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom). The Fund also may invest up to 35% of its total assets in companies in emerging markets (for example, China, India and Brazil). The Fund generally invests in at least three countries other than the United States but may invest up to 25% of its total assets in securities of U.S. issuers.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $25 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $25 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $25 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $25 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $25 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies. The Fund also may invest in larger-sized companies.

The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to invest in a limited number of foreign companies (generally between 40-60), offering the potential to provide above-average growth over time.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Risk [Heading]

rr_RiskHeading

Principal Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Performance Information

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart below shows you how the performance of the Fund's Class Z shares has varied from year to year.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800.345.6611

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.columbiamanagement.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Year by Year Total Return (%) as of December 31 Each Year

^[28]

Bar Chart Narrative [Text Block]

rr_BarChartNarrativeTextBlock

The bar chart below shows you how the performance of the Fund's Class Z shares has varied from year to year.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    23.44%

Worst:   3rd quarter 2008:   -24.76%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Return as of December 31, 2011

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

The table compares the Fund's returns, for each period, with those of the Standard & Poor's (S&P) Developed Ex-U.S. Between $2 Billion and $10 Billion® Index, the Fund's primary benchmark, and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index is a subset of the broad market selected by the index sponsor that represents the mid-cap developed market excluding the United States. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund's performance compares to a widely recognized broad based index of foreign market performance.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Acorn International Select Z) | (Columbia Acorn International Select) | S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(14.01%)

5 Years

rr_AverageAnnualReturnYear05

(3.06%)

10 Years

rr_AverageAnnualReturnYear10

8.41%

(Columbia Acorn International Select Z) | (Columbia Acorn International Select) | MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(12.14%)

5 Years

rr_AverageAnnualReturnYear05

(4.72%)

10 Years

rr_AverageAnnualReturnYear10

4.67%

(Columbia Acorn International Select Z) | (Columbia Acorn International Select) | Class Z Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

none

Management fees

rr_ManagementFeesOverAssets

0.94%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.31%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.25%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

127

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

397

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

686

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,511

Annual Return 2002

rr_AnnualReturn2002

(14.89%)

Annual Return 2003

rr_AnnualReturn2003

41.79%

Annual Return 2004

rr_AnnualReturn2004

24.14%

Annual Return 2005

rr_AnnualReturn2005

15.98%

Annual Return 2006

rr_AnnualReturn2006

36.27%

Annual Return 2007

rr_AnnualReturn2007

21.86%

Annual Return 2008

rr_AnnualReturn2008

(42.10%)

Annual Return 2009

rr_AnnualReturn2009

31.52%

Annual Return 2010

rr_AnnualReturn2010

21.89%

Annual Return 2011

rr_AnnualReturn2011

(9.76%)

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-date return as of March 31, 2012: 11.37%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

11.37%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

2nd quarter 2009:

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

23.44%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

3rd quarter 2008:

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(24.76%)

1 Year

rr_AverageAnnualReturnYear01

(9.76%)

5 Years

rr_AverageAnnualReturnYear05

0.41%

10 Years

rr_AverageAnnualReturnYear10

9.22%

(Columbia Acorn International Select Z) | (Columbia Acorn International Select) | Class Z Shares | returns after taxes on distributions

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(10.24%)

5 Years

rr_AverageAnnualReturnYear05

0.01%

10 Years

rr_AverageAnnualReturnYear10

9.02%

(Columbia Acorn International Select Z) | (Columbia Acorn International Select) | Class Z Shares | returns after taxes on distributions and sale of Fund shares

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(5.37%)

5 Years

rr_AverageAnnualReturnYear05

0.45%

10 Years

rr_AverageAnnualReturnYear10

8.31%

(Columbia Thermostat Fund A&C) | (Columbia Thermostat Fund)

Risk/Return:

rr_RiskReturnAbstract

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation.

Expense [Heading]

rr_ExpenseHeading

Fees and Expenses of the Fund

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds. More information about these and other discounts is available from your financial advisor, in the Choosing a Share Class section beginning on page 28 of this prospectus and in Appendix D to the Statement of Additional Information under Sales Charge Waivers beginning on page D-1.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

2013-04-30

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund will indirectly bear the expenses associated with portfolio turnover of the underlying Portfolio Funds in which the Fund invests. Each Portfolio Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A Portfolio Fund's higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when its shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 130% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

130.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class A or Class C shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire on April 30, 2013, they are only reflected in the 1 year example and the first year of the 3, 5 and 10 year examples.

Based on the assumptions listed above, your costs would be:

Expense Example Closing [Text Block]

rr_ExpenseExampleClosingTextBlock

Remember this is an example only. Your actual costs may be higher or lower.

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund pursues its investment objective by investing in other mutual funds. As a "fund of funds," under normal circumstances, the Fund allocates at least 95% of its net assets (stock/bond assets) among a selected group of stock and bond mutual funds (Portfolio Funds) according to the current level of Standard & Poor's (S&P) 500® Index. Generally, when the S&P 500® Index goes up in relation to predetermined ranges set by Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), the Fund sells a portion of its stock funds and invests more in the bond funds and when the S&P 500® Index goes down in relation to the ranges, the Fund increases its investment in the stock funds. Under normal circumstances, the Fund may invest up to 5% of net assets plus any cash received that day in cash, high quality short-term paper and government securities.

Many asset allocation funds typically move assets from stocks to bonds when the market goes up, and from bonds to stocks when the market goes down. Most asset allocation funds are run by sophisticated investment professionals, who make subjective decisions based on economic and financial data and complex graphs of market behavior. By contrast, the day-to-day investment decisions for the Fund are made according to a single predetermined rule. The temperature in your house is run by a single rule: your thermostat turns on the furnace if your house is too cold or turns on the air conditioner if your house is too warm. This Fund works the same way, so it is named Columbia Thermostat Fund.

Because the Fund invests according to a pre-set program, there is no need for subjective day-to-day management. Although another successful asset allocation strategy might do better than the Fund, the Fund is designed for those who doubt the wisdom of trying to "time" the market and are unsure of the long-term trend of the stock market. The Fund takes psychology out of investing; it avoids the temptation to buy more stocks because the stock market is currently going up or to sell stocks because the market is declining. The Fund operates continuously and substantially automatically, subject to periodic review of the pre-set program by the Investment Manager and the Fund's Board of Trustees. As described more fully below, the Investment Manager has the authority to review the structure and allocation ranges of the stock/bond allocation table and to make any changes considered appropriate.

The Investment Manager chooses the Portfolio Funds to provide participation in the major sectors of the stock and bond markets. If you believe that the stock market will tend to go up most of the time, then you should probably own a fully invested stock fund and use a buy-and-hold strategy. Buy-and-hold was an excellent strategy in the 1982-1999 bull market. However, there have been long periods in the past when buy-and-hold was not the best strategy, such as 1930-1954 and 1969-1981, when the market fluctuated but did not make significant new highs. The Fund may be a good investment choice for you if you believe that the market may fluctuate in a trading range for many years, that a remarkable bull market ended early in 2000 and that the market may not reach significant new highs for many years.

The Fund invests its stock/bond assets among the Portfolio Funds according to an asset allocation table. The current allocation table is set forth below.

Stock/Bond Allocation Table

                                      How the Fund will Invest the Stock/Bond Assets

                                      ----------------------------------------------



Level of the S and P 500(R) Index   	    Stock Percentage     Bond Percentage

---------------------------------           ----------------     ---------------

over 1750                                          10%                90%

over 1700 -- 1750                                  15%                85%

over 1650 -- 1700                                  20%                80%

over 1600 -- 1650                                  25%                75%

over 1550 -- 1600                                  30%                70%

over 1500 -- 1550                                  35%                65%

over 1450 -- 1500                                  40%                60%

over 1400 -- 1450                                  45%                55%

over 1350 -- 1400                                  50%                50%

over 1300 -- 1350                                  55%                45%

over 1250 -- 1300                                  60%                40%

over 1200 -- 1250                                  65%                35%

over 1150 -- 1200                                  70%                30%

over 1100 -- 1150                                  75%                25%

over 1050 -- 1100                                  80%                20%

over 1000 -- 1050                                  85%                15%

1000 and under                                     90%                10%

When the S&P 500® Index moves into a new band on the table, the Fund promptly will rebalance the stock/bond mix to reflect the new S&P 500® Index price level by redeeming shares of some Portfolio Funds and purchasing shares of other Portfolio Funds. The only exception will be a "31-day Rule"; in order to reduce taxable events, after the Fund has increased its percentage allocation to either stock funds or bond funds, it will not decrease that allocation for at least 31 days. Following a change in the Fund's stock/bond mix, if the S&P 500® Index remains within the same band for a while, normal market fluctuations will change the values of the Fund's holdings of stock Portfolio Funds and bond Portfolio Funds. The Investment Manager will invest cash flows from sales (or redemptions) of Fund shares to bring the stock/bond mix back toward the allocation percentages for that S&P 500® Index band. For example, if the S&P 500® Index is in the 1150-1200 band, and the value of the holdings of the stock Portfolio Funds has dropped to 68% of the value of the holdings of all Portfolio Funds, the Investment Manager would invest new cash in the stock Portfolio Funds (or cash for redemptions would come from the bond Portfolio Funds). If the 31-day Rule is in effect, the Investment Manager will invest new cash at the stock/bond percentage allocation as of the latest rebalancing.

As an illustrative example, suppose the following:

 		              Level of the 		           How the Fund will invest

Date		          S and P 500(R) Index                       the Stock/Bond Assets

--------        ---------------------------------------         --------------------------------

Nov. 1             We begin when the market is 1380                  50% stocks, 50% bonds

Dec. 1             The S and P 500(R) goes to 1401              rebalance 45% stocks, 55% bonds

Dec. 6           The S and P 500(R) drops back to 1390              no reversal for 31 days

Jan. 2              The S and P 500(R) is at 1352               rebalance 50% stocks, 50% bonds

Jan. 20            The S and P 500(R) drops to 1349             rebalance 55% stocks, 45% bonds



      The market has made a continuation move by going through a second action level,

          not a reversal move, so the 31-day Rule does not apply in this case.



Jan. 30            The S and P 500(R) goes up to 1355               no reversal for 31 days

Feb. 20              The S and P 500(R) is at 1360              rebalance 50% stocks, 50% bonds

The following table shows the seven stock Portfolio Funds and three bond Portfolio Funds that the Fund currently uses in its "fund of funds" structure and the current allocation percentage for each Portfolio Fund within the stock or bond category. As described more fully below, the Investment Manager may substitute or add additional Portfolio Funds at any time, including funds introduced after the date of this prospectus. The allocation percentage within each stock/bond category is achieved by rebalancing the investments within the category whenever the S&P 500® Index moves into a new band on the allocation table, subject to the 31-day Rule described above. The Fund does not liquidate its investment in one Portfolio Fund in order to invest in another Portfolio Fund except in connection with a rebalancing due to a move of the S&P 500® Index into a new band (or due to a change by the Investment Manager in the stock/bond allocation table to the Portfolio Funds or to the relative allocation among them). Until a subsequent rebalancing, the Fund's investments in, and redemptions from, the stock Portfolio Funds or the bond Portfolio Funds are allocated among the Portfolio Funds in a manner that will reduce any deviation of the relative values of the Fund's holdings of the Funds from the allocation percentages shown below.

Allocation of Stock/Bond Assets Within Asset Classes

Stock Funds                                   Type of Fund 	             Allocation

-------------------------------------  ------------------------------------  -----------

Columbia Acorn Fund                    Small/Mid-cap growth                          15%

Columbia Acorn Select                  Mid-cap growth                                10%

Columbia Acorn International           Small/Mid-cap international growth            20%

Columbia Dividend Income Fund          Large-cap value                               20%

Columbia Large Cap Enhanced Core Fund  Large-cap blend                               10%

Columbia Contrarian Core Fund          Large-cap blend                               15%

Columbia Select Large Cap Growth Fund  Large-cap growth                              10%

Total                                                                               100%



Bond Funds                                    Type of Fund 	             Allocation

-------------------------------------  ------------------------------------  -----------

Columbia Intermediate Bond Fund        Intermediate-term bonds                       50%

Columbia Income Opportunities Fund     High-yield bonds                              30%

Columbia U.S. Treasury Index Fund      U.S. Treasury notes/bonds                     20%

Total                                                                               100%

The Investment Manager has the authority to review the Portfolio Funds and the relative stock/bond allocation percentages among them and to make any changes considered appropriate.

Each of the Portfolio Funds is currently managed by the Investment Manager or its affiliates. The Fund does not pay any sales load on its purchases of shares of the Portfolio Funds. On an annual basis, or on an "emergency" basis if necessary, the Investment Manager reviews the structure, allocation percentages and Portfolio Funds and makes any changes considered appropriate. The Investment Manager typically addresses the following questions:

• Should the stock/bond allocation table be revised (perhaps because the stock market has made a long-term move outside of the bands set forth above)?
• Should there be a change in the Portfolio Funds or should there be a change in the percentage allocations among the stock/bond funds (perhaps because of a change of portfolio managers, change of investment style, change in relative valuation or a reorganization of a Portfolio Fund)?

Any such changes by the Investment Manager are expected to be infrequent.

Risk [Heading]

rr_RiskHeading

Principal Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Allocation Risk – The Fund uses an asset allocation strategy in pursuit of its investment objective. There is a risk that the Fund's allocation among asset classes or investments will cause the Fund's shares to lose value or cause the Fund to underperform other funds with similar investment objectives, or that the investments themselves will not produce the returns expected.

• Investing in Other Funds Risk – The performance of the underlying fund(s) in which the Fund invests could be adversely affected if other entities that invest in the same underlying fund(s) make relatively large investments or redemptions in the underlying fund(s). In addition, because the expenses and costs of the underlying fund(s) are shared by investors in the underlying fund, redemptions by other investors in the underlying fund could result in decreased economies of scale and increased operating expenses for the underlying fund. The Fund, and its shareholders, indirectly bear a portion of the expenses of the underlying fund(s). These transactions might also result in higher brokerage, tax or other costs for the Fund. This risk may be particularly important when one investor owns a substantial portion of any underlying fund. In addition, the Investment Manager has the authority to change the underlying fund(s) in which the Fund invests or to change the percentage of the Fund's investments allocated to each underlying fund. If an underlying fund pays fees to the Investment Manager or its affiliates, such as advisory fees, this could result in the Investment Manager having a potential conflict of interest in selecting the underlying fund(s) in which the Fund invests or in determining the percentage of the Fund's investments allocated to each underlying fund. In addition, the underlying funds are themselves subject to Investment Strategy Risk.

The Fund is subject indirectly to the following risks of the Portfolio Funds:

• Market Risk – Market risk refers to the possibility that the market values of securities that a Portfolio Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Portfolio Fund. Accordingly, an investment in a Portfolio Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Portfolio Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Interest Rate Risk – Debt securities are subject to interest rate risk. In general, if prevailing interest rates rise, the values of debt securities will tend to fall, and if interest rates fall, the values of debt securities will tend to rise. Changes in the value of a debt security usually will not affect the amount of income a Portfolio Fund receives from it but may affect the value of the Portfolio Fund's shares. Interest rate risk is generally greater for debt securities with longer maturities/durations.

• Credit Risk – Credit risk applies to most debt securities, but is generally less of a factor for obligations backed by the "full faith and credit" of the U.S. Government. A Portfolio Fund could lose money if the issuer of a debt security owned by the Fund is unable or perceived to be unable to pay interest or repay principal when it becomes due. Various factors could affect the issuer's actual or perceived willingness or ability to make timely interest or principal payments, including changes in the issuer's financial condition or in general economic conditions. Debt securities backed by an issuer's taxing authority may be subject to legal limits on the issuer's power to increase taxes or otherwise to raise revenue, or may be dependent on legislative appropriation or government aid. Certain debt securities are backed only by revenues derived from a particular project or source, rather than by an issuer's taxing authority, and thus may have a greater risk of default.

• Low and Below Investment Grade Securities Risk – Debt securities with the lowest investment grade rating (e.g., BBB by Standard & Poor's, a division of the McGraw-Hill Companies, Inc. (S&P), or Fitch, Inc. (Fitch) or Baa by Moody's Investors Service, Inc. (Moody's)), or that are below investment grade (which are commonly referred to as "junk bonds") (e.g., BB or below by S&P or Fitch or Ba by Moody's) and unrated securities of comparable quality are more speculative than securities with higher ratings and may experience greater price fluctuations. These securities tend to be more sensitive to credit risk than higher-rated securities, particularly during a downturn in the economy, which is more likely to weaken the ability of the issuers to make principal and interest payments on these securities. These securities typically pay a premium – a higher interest rate or yield – because of the increased risk of loss, including default. These securities also are generally less liquid than higher-rated securities. The securities ratings provided by Moody's, S&P and Fitch are based on analyses by these ratings agencies of the credit quality of the securities and may not take into account every risk related to whether interest or principal will be timely repaid.

• Value Securities Risk – Value securities are securities of companies that may have experienced, for example, adverse business, industry or other developments or may be subject to special risks that have caused the securities to be out of favor and, in turn, potentially undervalued. The market value of a portfolio security may not meet the Investment Manager's future value assessment of that security, or may decline. There is also a risk that it may take longer than expected for the value of these investments to rise to the believed value. In addition, value securities, at times, may not perform as well as growth securities or the stock market in general, and may be out of favor with investors for varying periods of time.

• Growth Securities Risk – Because growth securities typically trade at a higher multiple of earnings than other types of securities, the market values of growth securities may be more sensitive to changes in current or expected earnings than the market values of other types of securities. In addition, growth securities, at times, may not perform as well as value securities or the stock market in general, and may be out of favor with investors for varying periods of time.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Portfolio Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Portfolio Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Index Risk – U.S. Treasury Index Fund's value will generally decline when the performance of its targeted index declines. Because U.S. Treasury Index Fund is designed to track an index before fees and expenses, U.S. Treasury Index Fund cannot purchase other securities that may help offset declines in its index. In addition, because U.S. Treasury Index Fund may not hold all issues included in its index, may not always be fully invested, and bears advisory, administrative and other expenses and transaction costs in trading securities, U.S. Treasury Index Fund's performance may fail to match the performance of its targeted index, after taking expenses into account. It is not possible to invest directly in an index.

• U.S. Government Obligations Risk – While U.S. Treasury obligations are backed by the "full faith and credit" of the U.S. Government, such securities are nonetheless subject to credit risk (i.e., the risk that the U.S. Government may be, or may be perceived to be, unable or unwilling to honor its financial obligations, such as making payments). Securities issued or guaranteed by federal agencies or authorities and U.S. Government-sponsored instrumentalities or enterprises may or may not be backed by the full faith and credit of the U.S. Government. For example, securities issued by the Federal Home Loan Mortgage Corporation, the Federal National Mortgage Association and the Federal Home Loan Banks are neither insured nor guaranteed by the U.S. Government. These securities may be supported by the ability to borrow from the U.S. Treasury or only by the credit of the issuing agency, authority, instrumentality or enterprise and, as a result, are subject to greater credit risk than securities issued or guaranteed by the U.S. Treasury. Securities guaranteed by the Federal Deposit Insurance Corporation under its Temporary Liquidity Guarantee Program (TLGP) are subject to certain risks, including whether such securities will continue to trade in line with recent experience in relation to treasury and government agency securities in terms of yield spread and the volatility of such spread, as well as uncertainty as to how such securities will trade in the secondary market and whether that market will be liquid or illiquid. The TLGP is subject to change. See ABOUT THE FUNDS' INVESTMENTS - U.S. Government and Related Obligations in the Statement of Additional Information for more information.

• Derivatives Risk – Derivatives are financial contracts whose values are, for example, based on (or "derived" from) traditional securities (such as a stock or bond), assets (such as a commodity like gold or a foreign currency), reference rates (such as LIBOR) or market indices (such as the S&P 500® Index). Derivatives involve special risks and may result in losses or may limit a Portfolio Fund's potential gain from favorable market movements. Derivative strategies often involve leverage, which may exaggerate a loss, potentially causing a Portfolio Fund to lose more money than it would have lost had it invested in the underlying security or other asset. The values of derivatives may move in unexpected ways, especially in unusual market conditions, and may result in increased volatility, among other consequences. The use of derivatives may also increase the amount of taxes payable by shareholders holding shares in a taxable account. Other risks arise from a Portfolio Fund's potential inability to terminate or to sell derivative positions. A liquid secondary market may not always exist for the Portfolio Fund's derivative positions at times when the Portfolio Fund might wish to terminate or to sell such positions. Over-the-counter instruments (investments not traded on an exchange) may be illiquid, and transactions in derivatives traded in the over-the-counter market are subject to the risk that the other party will not meet its obligations. The use of derivatives also involves the risks of mispricing or improper valuation and that changes in the value of the derivative may not correlate perfectly with the underlying security, asset, reference rate or index. A Portfolio Fund also may not be able to find a suitable derivative transaction counterparty, and thus may be unable to engage in derivative transactions when it is deemed favorable to do so, or at all. U.S. federal legislation has recently been enacted that provides for new clearing, margin, reporting and registration requirements for participants in the derivatives market. While the ultimate impact is not yet clear, these changes could restrict and/or impose significant costs or other burdens upon the Fund's participation in derivatives transactions. For more information on the risks of derivative investments and strategies, see the Statement of Additional Information.

• Convertible Securities Risk – Certain Portfolio Funds invest in convertible securities, which are subject to the usual risks associated with debt securities, such as interest rate risk and credit risk. Convertible securities also react to changes in the value of the common stock into which they convert. Because the value of a convertible security can be influenced by both interest rates and the common stock's market movements, a convertible security generally is not as sensitive to interest rates as a similar debt security, and generally will not vary in value in response to other factors to the same extent as the underlying common stock. In the event of a liquidation of the issuing company, holders of convertible securities would typically be paid before the company's common stockholders but after holders of any senior debt obligations of the company. A Portfolio Fund may be forced to convert a convertible security before it otherwise would choose to do so, which may decrease the Portfolio Fund's return.

• Non-Diversified Mutual Fund Risk – If a Portfolio Fund is non-diversified, that Portfolio Fund generally may invest a greater percentage of its total assets in the securities of fewer issuers than may a "diversified" fund. This increases the risk that a change in the value of any one investment held by the non-diversified Portfolio Fund could affect the overall value of the Portfolio Fund more than it would affect that of a diversified fund holding a greater number of investments. Accordingly, a non-diversified Portfolio Fund's value will likely be more volatile than the value of more diversified funds. A Portfolio Fund that is non-diversified may not operate as a non-diversified fund at all times.

• Technology Sector Risk – Companies in the technology sector are subject to significant competitive pressures, such as aggressive pricing of their products or services, new market entrants, competition for market share, short product cycles due to an accelerated rate of technological developments and the potential for limited earnings and/or falling profit margins. These companies also face the risks that new services, equipment or technologies will not be accepted by consumers and businesses or will become rapidly obsolete. These factors can affect the profitability of technology companies and, as a result, the value of their securities. Also, patent protection is integral to the success of many companies in the technology sector, and profitability can be affected materially by, among other things, the cost of obtaining (or failing to obtain) patent approvals, the cost of litigating patent infringement and the loss of patent protection for products (which significantly increases pricing pressures and can materially reduce profitability with respect to such products). In addition, many technology companies have limited operating histories. Prices of these companies' securities historically have been more volatile than other securities, especially over the short term. Because certain Portfolio Funds invest a significant portion of their net assets in the equity securities of technology companies, a Portfolio Fund's price may be more volatile than a fund that is invested in a more diverse range of market sectors.

• Health Care Sector Risk - Companies in the health care sector are subject to extensive government regulation. Their profitability can be affected significantly and adversely by restrictions on government reimbursement for medical expenses, government approval of medical products and services, competitive pricing pressures, an increased emphasis on outpatient and other alternative services and other factors. Patent protection is integral to the success of companies in the health care sector, and profitability can be affected materially by, among other things, the cost of obtaining (or failing to obtain) patent approvals, the cost of litigating patent infringement and the loss of patent protection for medical products (which significantly increases pricing pressures and can materially reduce profitability with respect to such products). Companies in the health care sector also potentially are subject to extensive product liability and other similar litigation. Companies in the health care sector are affected by the rising cost of medical products and services, and the effects of such rising costs can be particularly pronounced for companies that are dependent on a relatively limited number of products or services. Medical products also frequently become obsolete due to industry innovation or other causes. Because certain Portfolio Funds invest a significant portion of their net assets in the equity securities of health care companies, a Portfolio Fund's price may be more volatile than a fund that is invested in a more diverse range of market sectors.

Risk Nondiversified Status [Text]

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Non-Diversified Mutual Fund Risk – If a Portfolio Fund is non-diversified, that Portfolio Fund generally may invest a greater percentage of its total assets in the securities of fewer issuers than may a "diversified" fund. This increases the risk that a change in the value of any one investment held by the non-diversified Portfolio Fund could affect the overall value of the Portfolio Fund more than it would affect that of a diversified fund holding a greater number of investments. Accordingly, a non-diversified Portfolio Fund's value will likely be more volatile than the value of more diversified funds. A Portfolio Fund that is non-diversified may not operate as a non-diversified fund at all times.

Bar Chart and Performance Table [Heading]

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Performance Information

Performance Narrative [Text Block]

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The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The inception date for the Fund's Class A and Class C shares is March 3, 2003. The returns shown for these share classes include the returns of the Fund's Class Z shares (adjusted to reflect the higher class-related operating expenses of such classes, where applicable) for periods from the inception date of Class Z shares (September 25, 2002) to the inception of these classes. Except for differences in expenses and sales charges (where applicable), these classes of shares have annual returns substantially similar to those of Class Z shares, which are not offered in this prospectus, because all classes of the Fund's shares invest in the same portfolio of securities.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart below shows you how the performance of the Fund's Class A shares has varied from year to year.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800.345.6611

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.columbiamanagement.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.

Bar Chart [Heading]

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Year by Year Total Return (%) as of December 31 Each Year

^[29]

Bar Chart Narrative [Text Block]

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The bar chart below shows you how the performance of the Fund's Class A shares has varied from year to year. These returns do not reflect deductions of sales charges, if any, paid by investors and would be lower if they did.

Bar Chart Closing [Text Block]

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Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    19.22%

Worst:   4th quarter 2008:   -19.26%

Performance Table Heading

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Average Annual Total Return as of December 31, 2011

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Performance Table One Class of after Tax Shown [Text]

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The after-tax returns are shown only for Class A shares and will vary for other share classes.

Performance Table Explanation after Tax Higher

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Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

Performance Table Narrative

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The table compares the Fund's returns for each period with those of the S&P 500® Index, the Fund's primary benchmark for equity securities, the Barclays U.S. Aggregate Bond Index, the Fund's primary benchmark for debt securities, the Lipper Flexible Portfolio Funds Index and a 50/50 Blended Benchmark. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. The Barclays U.S. Aggregate Bond Index is a market value-weighted index that tracks the daily price, coupon, pay-downs, and total return performance of fixed-rate, publicly placed, dollar-denominated, and non-convertible investment grade debt issues with at least $250 million par amount outstanding and with at least one year to final maturity. The Lipper Flexible Portfolio Funds Index is an equal-weighted index of the 30 largest mutual funds within the Flexible Portfolio fund classification, as defined by Lipper, and shows how the Fund's performance compares with the returns of an index of funds with similar investment objectives. The 50/50 Blended Benchmark was established by the Investment Manager to show how the Fund's performance compares to an equally weighted custom composite of the Fund's primary equity and primary debt benchmarks, the S&P 500® Index and the Barclays U.S. Aggregate Bond Index, respectively. The percentage of the Fund's assets allocated to underlying stock and bond Portfolio Funds will vary, and accordingly the composition of the Fund's portfolio will not always reflect the composition of the 50/50 Blended Benchmark.

Performance Table Closing [Text Block]

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The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown only for Class A shares and will vary for other share classes.

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Thermostat Fund A&C) | (Columbia Thermostat Fund) | Barclays U.S. Aggregate Bond Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

7.84%

5 Years

rr_AverageAnnualReturnYear05

6.50%

Life of Fund

rr_AverageAnnualReturnSinceInception

5.33%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 25, 2002

(Columbia Thermostat Fund A&C) | (Columbia Thermostat Fund) | 50-50 S&P 500/Barclays Capital Aggregate Bond (an equally weighted custom composite of the Fund's primary benchmarks for equity and debt securities, established by the Investment Manager; reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

5.28%

5 Years

rr_AverageAnnualReturnYear05

3.54%

Life of Fund

rr_AverageAnnualReturnSinceInception

6.43%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 25, 2002

(Columbia Thermostat Fund A&C) | (Columbia Thermostat Fund) | Lipper Flexible Portfolio Funds Index (reflects no deductions for taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(1.16%)

5 Years

rr_AverageAnnualReturnYear05

2.02%

Life of Fund

rr_AverageAnnualReturnSinceInception

7.10%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 25, 2002

(Columbia Thermostat Fund A&C) | (Columbia Thermostat Fund) | S&P 500® Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

2.11%

5 Years

rr_AverageAnnualReturnYear05

(0.25%)

Life of Fund

rr_AverageAnnualReturnSinceInception

6.85%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 25, 2002

(Columbia Thermostat Fund A&C) | (Columbia Thermostat Fund) | Class A Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[1]

Management fees

rr_ManagementFeesOverAssets

0.10%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.46%

^[4]

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.65%

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.46%

^[5]

Fee waivers and/or reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.31%)

^[9]

Total annual Fund operating expenses after fee waivers and/or reimbursements

rr_NetExpensesOverAssets

1.15%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

685

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

981

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,299

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,196

Annual Return 2003

rr_AnnualReturn2003

19.39%

Annual Return 2004

rr_AnnualReturn2004

8.92%

Annual Return 2005

rr_AnnualReturn2005

5.25%

Annual Return 2006

rr_AnnualReturn2006

10.56%

Annual Return 2007

rr_AnnualReturn2007

8.19%

Annual Return 2008

rr_AnnualReturn2008

(30.67%)

Annual Return 2009

rr_AnnualReturn2009

31.98%

Annual Return 2010

rr_AnnualReturn2010

17.28%

Annual Return 2011

rr_AnnualReturn2011

4.62%

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-date return as of March 31, 2012: 8.19%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

8.19%

Highest Quarterly Return, Label

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2nd quarter 2009:

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

19.22%

Lowest Quarterly Return, Label

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4th quarter 2008:

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(19.26%)

1 Year

rr_AverageAnnualReturnYear01

(1.41%)

5 Years

rr_AverageAnnualReturnYear05

2.74%

Life of Fund

rr_AverageAnnualReturnSinceInception

6.56%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 25, 2002

(Columbia Thermostat Fund A&C) | (Columbia Thermostat Fund) | Class A Shares | returns after taxes on distributions

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(2.31%)

5 Years

rr_AverageAnnualReturnYear05

1.77%

Life of Fund

rr_AverageAnnualReturnSinceInception

5.42%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 25, 2002

(Columbia Thermostat Fund A&C) | (Columbia Thermostat Fund) | Class A Shares | returns after taxes on distributions and sale of Fund shares

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(0.92%)

5 Years

rr_AverageAnnualReturnYear05

1.85%

Life of Fund

rr_AverageAnnualReturnSinceInception

5.18%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 25, 2002

(Columbia Thermostat Fund A&C) | (Columbia Thermostat Fund) | Class C Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[2]

Management fees

rr_ManagementFeesOverAssets

0.10%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other expenses

rr_OtherExpensesOverAssets

0.46%

^[4]

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.65%

Total annual Fund operating expenses

rr_ExpensesOverAssets

2.21%

^[5]

Fee waivers and/or reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.31%)

^[9]

Total annual Fund operating expenses after fee waivers and/or reimbursements

rr_NetExpensesOverAssets

1.90%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

293

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

661

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,156

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,520

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

193

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

661

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

1,156

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

2,520

1 Year

rr_AverageAnnualReturnYear01

2.87%

5 Years

rr_AverageAnnualReturnYear05

3.19%

Life of Fund

rr_AverageAnnualReturnSinceInception

6.45%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 25, 2002

(Columbia Thermostat Fund B) | (Columbia Thermostat Fund)

Risk/Return:

rr_RiskReturnAbstract

Objective [Heading]

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Investment Objective

Objective, Primary [Text Block]

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The Fund seeks long-term capital appreciation.

Expense [Heading]

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Fees and Expenses of the Fund

Expense Narrative [Text Block]

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This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

2013-04-30

Portfolio Turnover [Heading]

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Portfolio Turnover

Portfolio Turnover [Text Block]

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The Fund will indirectly bear the expenses associated with portfolio turnover of the underlying Portfolio Funds in which the Fund invests. Each Portfolio Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A Portfolio Fund's higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when its shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 130% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

130.00%

Expense Example [Heading]

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Example

Expense Example Narrative [Text Block]

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The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class B shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire on April 30, 2013, they are only reflected in the 1 year example and the first year of the 3, 5 and 10 year examples.

Based on the assumptions listed above, your costs would be:

Expense Example Closing [Text Block]

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Remember this is an example only. Your actual costs may be higher or lower.

Strategy [Heading]

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Principal Investment Strategies

Strategy Narrative [Text Block]

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The Fund pursues its investment objective by investing in other mutual funds. As a "fund of funds," under normal circumstances, the Fund allocates at least 95% of its net assets (stock/bond assets) among a selected group of stock and bond mutual funds (Portfolio Funds) according to the current level of Standard & Poor's (S&P) 500® Index. Generally, when the S&P 500® Index goes up in relation to predetermined ranges set by Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), the Fund sells a portion of its stock funds and invests more in the bond funds and when the S&P 500® Index goes down in relation to the ranges, the Fund increases its investment in the stock funds. Under normal circumstances, the Fund may invest up to 5% of net assets plus any cash received that day in cash, high quality short-term paper and government securities.

Many asset allocation funds typically move assets from stocks to bonds when the market goes up, and from bonds to stocks when the market goes down. Most asset allocation funds are run by sophisticated investment professionals, who make subjective decisions based on economic and financial data and complex graphs of market behavior. By contrast, the day-to-day investment decisions for the Fund are made according to a single predetermined rule. The temperature in your house is run by a single rule: your thermostat turns on the furnace if your house is too cold or turns on the air conditioner if your house is too warm. This Fund works the same way, so it is named Columbia Thermostat Fund.

Because the Fund invests according to a pre-set program, there is no need for subjective day-to-day management. Although another successful asset allocation strategy might do better than the Fund, the Fund is designed for those who doubt the wisdom of trying to "time" the market and are unsure of the long-term trend of the stock market. The Fund takes psychology out of investing; it avoids the temptation to buy more stocks because the stock market is currently going up or to sell stocks because the market is declining. The Fund operates continuously and substantially automatically, subject to periodic review of the pre-set program by the Investment Manager and the Fund's Board of Trustees. As described more fully below, the Investment Manager has the authority to review the structure and allocation ranges of the stock/bond allocation table and to make any changes considered appropriate.

The Investment Manager chooses the Portfolio Funds to provide participation in the major sectors of the stock and bond markets. If you believe that the stock market will tend to go up most of the time, then you should probably own a fully invested stock fund and use a buy-and-hold strategy. Buy-and-hold was an excellent strategy in the 1982-1999 bull market. However, there have been long periods in the past when buy-and-hold was not the best strategy, such as 1930-1954 and 1969-1981, when the market fluctuated but did not make significant new highs. The Fund may be a good investment choice for you if you believe that the market may fluctuate in a trading range for many years, that a remarkable bull market ended early in 2000 and that the market may not reach significant new highs for many years.

The Fund invests its stock/bond assets among the Portfolio Funds according to an asset allocation table. The current allocation table is set forth below.

Stock/Bond Allocation Table

                                      How the Fund will Invest the Stock/Bond Assets

                                      ----------------------------------------------



Level of the S and P 500(R) Index   	    Stock Percentage     Bond Percentage

---------------------------------           ----------------     ---------------

over 1750                                          10%                90%

over 1700 -- 1750                                  15%                85%

over 1650 -- 1700                                  20%                80%

over 1600 -- 1650                                  25%                75%

over 1550 -- 1600                                  30%                70%

over 1500 -- 1550                                  35%                65%

over 1450 -- 1500                                  40%                60%

over 1400 -- 1450                                  45%                55%

over 1350 -- 1400                                  50%                50%

over 1300 -- 1350                                  55%                45%

over 1250 -- 1300                                  60%                40%

over 1200 -- 1250                                  65%                35%

over 1150 -- 1200                                  70%                30%

over 1100 -- 1150                                  75%                25%

over 1050 -- 1100                                  80%                20%

over 1000 -- 1050                                  85%                15%

1000 and under                                     90%                10%

When the S&P 500® Index moves into a new band on the table, the Fund promptly will rebalance the stock/bond mix to reflect the new S&P 500® Index price level by redeeming shares of some Portfolio Funds and purchasing shares of other Portfolio Funds. The only exception will be a "31-day Rule"; in order to reduce taxable events, after the Fund has increased its percentage allocation to either stock funds or bond funds, it will not decrease that allocation for at least 31 days. Following a change in the Fund's stock/bond mix, if the S&P 500® Index remains within the same band for a while, normal market fluctuations will change the values of the Fund's holdings of stock Portfolio Funds and bond Portfolio Funds. The Investment Manager will invest cash flows from sales (or redemptions) of Fund shares to bring the stock/bond mix back toward the allocation percentages for that S&P 500® Index band. For example, if the S&P 500® Index is in the 1150-1200 band, and the value of the holdings of the stock Portfolio Funds has dropped to 68% of the value of the holdings of all Portfolio Funds, the Investment Manager would invest new cash in the stock Portfolio Funds (or cash for redemptions would come from the bond Portfolio Funds). If the 31-day Rule is in effect, the Investment Manager will invest new cash at the stock/bond percentage allocation as of the latest rebalancing.

As an illustrative example, suppose the following:

 		              Level of the 		           How the Fund will invest

Date		          S and P 500(R) Index                       the Stock/Bond Assets

--------        ---------------------------------------         --------------------------------

Nov. 1             We begin when the market is 1380                  50% stocks, 50% bonds

Dec. 1             The S and P 500(R) goes to 1401              rebalance 45% stocks, 55% bonds

Dec. 6           The S and P 500(R) drops back to 1390              no reversal for 31 days

Jan. 2              The S and P 500(R) is at 1352               rebalance 50% stocks, 50% bonds

Jan. 20            The S and P 500(R) drops to 1349             rebalance 55% stocks, 45% bonds



      The market has made a continuation move by going through a second action level,

          not a reversal move, so the 31-day Rule does not apply in this case.



Jan. 30            The S and P 500(R) goes up to 1355               no reversal for 31 days

Feb. 20              The S and P 500(R) is at 1360              rebalance 50% stocks, 50% bonds

The following table shows the seven stock Portfolio Funds and three bond Portfolio Funds that the Fund currently uses in its "fund of funds" structure and the current allocation percentage for each Portfolio Fund within the stock or bond category. As described more fully below, the Investment Manager may substitute or add additional Portfolio Funds at any time, including funds introduced after the date of this prospectus. The allocation percentage within each stock/bond category is achieved by rebalancing the investments within the category whenever the S&P 500® Index moves into a new band on the allocation table, subject to the 31-day Rule described above. The Fund does not liquidate its investment in one Portfolio Fund in order to invest in another Portfolio Fund except in connection with a rebalancing due to a move of the S&P 500® Index into a new band (or due to a change by the Investment Manager in the stock/bond allocation table to the Portfolio Funds or to the relative allocation among them). Until a subsequent rebalancing, the Fund's investments in, and redemptions from, the stock Portfolio Funds or the bond Portfolio Funds are allocated among the Portfolio Funds in a manner that will reduce any deviation of the relative values of the Fund's holdings of the Funds from the allocation percentages shown below.

Allocation of Stock/Bond Assets Within Asset Classes

Stock Funds                                   Type of Fund 	             Allocation

-------------------------------------  ------------------------------------  -----------

Columbia Acorn Fund                    Small/Mid-cap growth                          15%

Columbia Acorn Select                  Mid-cap growth                                10%

Columbia Acorn International           Small/Mid-cap international growth            20%

Columbia Dividend Income Fund          Large-cap value                               20%

Columbia Large Cap Enhanced Core Fund  Large-cap blend                               10%

Columbia Contrarian Core Fund          Large-cap blend                               15%

Columbia Select Large Cap Growth Fund  Large-cap growth                              10%

Total                                                                               100%



Bond Funds                                    Type of Fund 	             Allocation

-------------------------------------  ------------------------------------  -----------

Columbia Intermediate Bond Fund        Intermediate-term bonds                       50%

Columbia Income Opportunities Fund     High-yield bonds                              30%

Columbia U.S. Treasury Index Fund      U.S. Treasury notes/bonds                     20%

Total                                                                               100%

The Investment Manager has the authority to review the Portfolio Funds and the relative stock/bond allocation percentages among them and to make any changes considered appropriate.

Each of the Portfolio Funds is currently managed by the Investment Manager or its affiliates. The Fund does not pay any sales load on its purchases of shares of the Portfolio Funds. On an annual basis, or on an "emergency" basis if necessary, the Investment Manager reviews the structure, allocation percentages and Portfolio Funds and makes any changes considered appropriate. The Investment Manager typically addresses the following questions:

• Should the stock/bond allocation table be revised (perhaps because the stock market has made a long-term move outside of the bands set forth above)?
• Should there be a change in the Portfolio Funds or should there be a change in the percentage allocations among the stock/bond funds (perhaps because of a change of portfolio managers, change of investment style, change in relative valuation or a reorganization of a Portfolio Fund)?

Any such changes by the Investment Manager are expected to be infrequent.

Risk [Heading]

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Principal Risks

Risk Narrative [Text Block]

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• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Allocation Risk – The Fund uses an asset allocation strategy in pursuit of its investment objective. There is a risk that the Fund's allocation among asset classes or investments will cause the Fund's shares to lose value or cause the Fund to underperform other funds with similar investment objectives, or that the investments themselves will not produce the returns expected.

• Investing in Other Funds Risk – The performance of the underlying fund(s) in which the Fund invests could be adversely affected if other entities that invest in the same underlying fund(s) make relatively large investments or redemptions in the underlying fund(s). In addition, because the expenses and costs of the underlying fund(s) are shared by investors in the underlying fund, redemptions by other investors in the underlying fund could result in decreased economies of scale and increased operating expenses for the underlying fund. The Fund, and its shareholders, indirectly bear a portion of the expenses of the underlying fund(s). These transactions might also result in higher brokerage, tax or other costs for the Fund. This risk may be particularly important when one investor owns a substantial portion of any underlying fund. In addition, the Investment Manager has the authority to change the underlying fund(s) in which the Fund invests or to change the percentage of the Fund's investments allocated to each underlying fund. If an underlying fund pays fees to the Investment Manager or its affiliates, such as advisory fees, this could result in the Investment Manager having a potential conflict of interest in selecting the underlying fund(s) in which the Fund invests or in determining the percentage of the Fund's investments allocated to each underlying fund. In addition, the underlying funds are themselves subject to Investment Strategy Risk.

The Fund is subject indirectly to the following risks of the Portfolio Funds:

• Market Risk – Market risk refers to the possibility that the market values of securities that a Portfolio Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Portfolio Fund. Accordingly, an investment in a Portfolio Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Portfolio Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Interest Rate Risk – Debt securities are subject to interest rate risk. In general, if prevailing interest rates rise, the values of debt securities will tend to fall, and if interest rates fall, the values of debt securities will tend to rise. Changes in the value of a debt security usually will not affect the amount of income a Portfolio Fund receives from it but may affect the value of the Portfolio Fund's shares. Interest rate risk is generally greater for debt securities with longer maturities/durations.

• Credit Risk – Credit risk applies to most debt securities, but is generally less of a factor for obligations backed by the "full faith and credit" of the U.S. Government. A Portfolio Fund could lose money if the issuer of a debt security owned by the Fund is unable or perceived to be unable to pay interest or repay principal when it becomes due. Various factors could affect the issuer's actual or perceived willingness or ability to make timely interest or principal payments, including changes in the issuer's financial condition or in general economic conditions. Debt securities backed by an issuer's taxing authority may be subject to legal limits on the issuer's power to increase taxes or otherwise to raise revenue, or may be dependent on legislative appropriation or government aid. Certain debt securities are backed only by revenues derived from a particular project or source, rather than by an issuer's taxing authority, and thus may have a greater risk of default.

• Low and Below Investment Grade Securities Risk – Debt securities with the lowest investment grade rating (e.g., BBB by Standard & Poor's, a division of the McGraw-Hill Companies, Inc. (S&P), or Fitch, Inc. (Fitch) or Baa by Moody's Investors Service, Inc. (Moody's)), or that are below investment grade (which are commonly referred to as "junk bonds") (e.g., BB or below by S&P or Fitch or Ba by Moody's) and unrated securities of comparable quality are more speculative than securities with higher ratings and may experience greater price fluctuations. These securities tend to be more sensitive to credit risk than higher-rated securities, particularly during a downturn in the economy, which is more likely to weaken the ability of the issuers to make principal and interest payments on these securities. These securities typically pay a premium – a higher interest rate or yield – because of the increased risk of loss, including default. These securities also are generally less liquid than higher-rated securities. The securities ratings provided by Moody's, S&P and Fitch are based on analyses by these ratings agencies of the credit quality of the securities and may not take into account every risk related to whether interest or principal will be timely repaid.

• Value Securities Risk – Value securities are securities of companies that may have experienced, for example, adverse business, industry or other developments or may be subject to special risks that have caused the securities to be out of favor and, in turn, potentially undervalued. The market value of a portfolio security may not meet the Investment Manager's future value assessment of that security, or may decline. There is also a risk that it may take longer than expected for the value of these investments to rise to the believed value. In addition, value securities, at times, may not perform as well as growth securities or the stock market in general, and may be out of favor with investors for varying periods of time.

• Growth Securities Risk – Because growth securities typically trade at a higher multiple of earnings than other types of securities, the market values of growth securities may be more sensitive to changes in current or expected earnings than the market values of other types of securities. In addition, growth securities, at times, may not perform as well as value securities or the stock market in general, and may be out of favor with investors for varying periods of time.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Portfolio Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Portfolio Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Index Risk – U.S. Treasury Index Fund's value will generally decline when the performance of its targeted index declines. Because U.S. Treasury Index Fund is designed to track an index before fees and expenses, U.S. Treasury Index Fund cannot purchase other securities that may help offset declines in its index. In addition, because U.S. Treasury Index Fund may not hold all issues included in its index, may not always be fully invested, and bears advisory, administrative and other expenses and transaction costs in trading securities, U.S. Treasury Index Fund's performance may fail to match the performance of its targeted index, after taking expenses into account. It is not possible to invest directly in an index.

• U.S. Government Obligations Risk – While U.S. Treasury obligations are backed by the "full faith and credit" of the U.S. Government, such securities are nonetheless subject to credit risk (i.e., the risk that the U.S. Government may be, or may be perceived to be, unable or unwilling to honor its financial obligations, such as making payments). Securities issued or guaranteed by federal agencies or authorities and U.S. Government-sponsored instrumentalities or enterprises may or may not be backed by the full faith and credit of the U.S. Government. For example, securities issued by the Federal Home Loan Mortgage Corporation, the Federal National Mortgage Association and the Federal Home Loan Banks are neither insured nor guaranteed by the U.S. Government. These securities may be supported by the ability to borrow from the U.S. Treasury or only by the credit of the issuing agency, authority, instrumentality or enterprise and, as a result, are subject to greater credit risk than securities issued or guaranteed by the U.S. Treasury. Securities guaranteed by the Federal Deposit Insurance Corporation under its Temporary Liquidity Guarantee Program (TLGP) are subject to certain risks, including whether such securities will continue to trade in line with recent experience in relation to treasury and government agency securities in terms of yield spread and the volatility of such spread, as well as uncertainty as to how such securities will trade in the secondary market and whether that market will be liquid or illiquid. The TLGP is subject to change. See ABOUT THE FUNDS' INVESTMENTS - U.S. Government and Related Obligations in the Statement of Additional Information for more information.

• Derivatives Risk – Derivatives are financial contracts whose values are, for example, based on (or "derived" from) traditional securities (such as a stock or bond), assets (such as a commodity like gold or a foreign currency), reference rates (such as LIBOR) or market indices (such as the S&P 500® Index). Derivatives involve special risks and may result in losses or may limit a Portfolio Fund's potential gain from favorable market movements. Derivative strategies often involve leverage, which may exaggerate a loss, potentially causing a Portfolio Fund to lose more money than it would have lost had it invested in the underlying security or other asset. The values of derivatives may move in unexpected ways, especially in unusual market conditions, and may result in increased volatility, among other consequences. The use of derivatives may also increase the amount of taxes payable by shareholders holding shares in a taxable account. Other risks arise from a Portfolio Fund's potential inability to terminate or to sell derivative positions. A liquid secondary market may not always exist for the Portfolio Fund's derivative positions at times when the Portfolio Fund might wish to terminate or to sell such positions. Over-the-counter instruments (investments not traded on an exchange) may be illiquid, and transactions in derivatives traded in the over-the-counter market are subject to the risk that the other party will not meet its obligations. The use of derivatives also involves the risks of mispricing or improper valuation and that changes in the value of the derivative may not correlate perfectly with the underlying security, asset, reference rate or index. A Portfolio Fund also may not be able to find a suitable derivative transaction counterparty, and thus may be unable to engage in derivative transactions when it is deemed favorable to do so, or at all. U.S. federal legislation has recently been enacted that provides for new clearing, margin, reporting and registration requirements for participants in the derivatives market. While the ultimate impact is not yet clear, these changes could restrict and/or impose significant costs or other burdens upon the Fund's participation in derivatives transactions. For more information on the risks of derivative investments and strategies, see the Statement of Additional Information.

• Convertible Securities Risk – Certain Portfolio Funds invest in convertible securities, which are subject to the usual risks associated with debt securities, such as interest rate risk and credit risk. Convertible securities also react to changes in the value of the common stock into which they convert. Because the value of a convertible security can be influenced by both interest rates and the common stock's market movements, a convertible security generally is not as sensitive to interest rates as a similar debt security, and generally will not vary in value in response to other factors to the same extent as the underlying common stock. In the event of a liquidation of the issuing company, holders of convertible securities would typically be paid before the company's common stockholders but after holders of any senior debt obligations of the company. A Portfolio Fund may be forced to convert a convertible security before it otherwise would choose to do so, which may decrease the Portfolio Fund's return.

• Non-Diversified Mutual Fund Risk – If a Portfolio Fund is non-diversified, that Portfolio Fund generally may invest a greater percentage of its total assets in the securities of fewer issuers than may a "diversified" fund. This increases the risk that a change in the value of any one investment held by the non-diversified Portfolio Fund could affect the overall value of the Portfolio Fund more than it would affect that of a diversified fund holding a greater number of investments. Accordingly, a non-diversified Portfolio Fund's value will likely be more volatile than the value of more diversified funds. A Portfolio Fund that is non-diversified may not operate as a non-diversified fund at all times.

• Technology Sector Risk – Companies in the technology sector are subject to significant competitive pressures, such as aggressive pricing of their products or services, new market entrants, competition for market share, short product cycles due to an accelerated rate of technological developments and the potential for limited earnings and/or falling profit margins. These companies also face the risks that new services, equipment or technologies will not be accepted by consumers and businesses or will become rapidly obsolete. These factors can affect the profitability of technology companies and, as a result, the value of their securities. Also, patent protection is integral to the success of many companies in the technology sector, and profitability can be affected materially by, among other things, the cost of obtaining (or failing to obtain) patent approvals, the cost of litigating patent infringement and the loss of patent protection for products (which significantly increases pricing pressures and can materially reduce profitability with respect to such products). In addition, many technology companies have limited operating histories. Prices of these companies' securities historically have been more volatile than other securities, especially over the short term. Because certain Portfolio Funds invest a significant portion of their net assets in the equity securities of technology companies, a Portfolio Fund's price may be more volatile than a fund that is invested in a more diverse range of market sectors.

• Health Care Sector Risk - Companies in the health care sector are subject to extensive government regulation. Their profitability can be affected significantly and adversely by restrictions on government reimbursement for medical expenses, government approval of medical products and services, competitive pricing pressures, an increased emphasis on outpatient and other alternative services and other factors. Patent protection is integral to the success of companies in the health care sector, and profitability can be affected materially by, among other things, the cost of obtaining (or failing to obtain) patent approvals, the cost of litigating patent infringement and the loss of patent protection for medical products (which significantly increases pricing pressures and can materially reduce profitability with respect to such products). Companies in the health care sector also potentially are subject to extensive product liability and other similar litigation. Companies in the health care sector are affected by the rising cost of medical products and services, and the effects of such rising costs can be particularly pronounced for companies that are dependent on a relatively limited number of products or services. Medical products also frequently become obsolete due to industry innovation or other causes. Because certain Portfolio Funds invest a significant portion of their net assets in the equity securities of health care companies, a Portfolio Fund's price may be more volatile than a fund that is invested in a more diverse range of market sectors.

Risk Nondiversified Status [Text]

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Non-Diversified Mutual Fund Risk – If a Portfolio Fund is non-diversified, that Portfolio Fund generally may invest a greater percentage of its total assets in the securities of fewer issuers than may a "diversified" fund. This increases the risk that a change in the value of any one investment held by the non-diversified Portfolio Fund could affect the overall value of the Portfolio Fund more than it would affect that of a diversified fund holding a greater number of investments. Accordingly, a non-diversified Portfolio Fund's value will likely be more volatile than the value of more diversified funds. A Portfolio Fund that is non-diversified may not operate as a non-diversified fund at all times.

Bar Chart and Performance Table [Heading]

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Performance Information

Performance Narrative [Text Block]

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The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The inception date for the Fund's Class B shares is March 3, 2003. The returns shown for this share class include the returns of the Fund's Class Z shares (adjusted to reflect the higher class-related operating expenses of Class B shares) for periods from the inception date of Class Z shares (September 25, 2002) to the inception date of Class B shares. Except for differences in expenses and sales charges, Class B shares have annual returns substantially similar to those of Class Z shares, which are not offered in this prospectus, because all classes of the Fund's shares invest in the same portfolio of securities.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

Performance Information Illustrates Variability of Returns [Text]

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The bar chart below shows you how the performance of the Fund's Class B shares has varied from year to year.

Performance Availability Phone [Text]

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800.345.6611

Performance Availability Website Address [Text]

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www.columbiamanagement.com

Performance Past Does Not Indicate Future [Text]

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The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.

Bar Chart [Heading]

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Year by Year Total Return (%) as of December 31 Each Year

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Bar Chart Narrative [Text Block]

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The bar chart below shows you how the performance of the Fund's Class B shares has varied from year to year.

Bar Chart Closing [Text Block]

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Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    19.07%

Worst:   4th quarter 2008:   -19.47%

Performance Table Heading

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Average Annual Total Return as of December 31, 2011

Performance Table Uses Highest Federal Rate

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The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.

Performance Table Not Relevant to Tax Deferred

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In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Performance Table Explanation after Tax Higher

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Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

Performance Table Narrative

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The table compares the Fund's returns for each period with those of the S&P 500® Index, the Fund's primary benchmark for equity securities, the Barclays U.S. Aggregate Bond Index, the Fund's primary benchmark for debt securities, the Lipper Flexible Portfolio Funds Index and a 50/50 Blended Benchmark. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. The Barclays U.S. Aggregate Bond Index is a market value-weighted index that tracks the daily price, coupon, pay-downs, and total return performance of fixed-rate, publicly placed, dollar-denominated, and non-convertible investment grade debt issues with at least $250 million par amount outstanding and with at least one year to final maturity. The Lipper Flexible Portfolio Funds Index is an equal-weighted index of the 30 largest mutual funds within the Flexible Portfolio fund classification, as defined by Lipper, and shows how the Fund's performance compares with the returns of an index of funds with similar investment objectives. The 50/50 Blended Benchmark was established by the Investment Manager to show how the Fund's performance compares to an equally weighted custom composite of the Fund's primary equity and primary debt benchmarks, the S&P 500® Index and the Barclays U.S. Aggregate Bond Index, respectively. The percentage of the Fund's assets allocated to underlying stock and bond Portfolio Funds will vary, and accordingly the composition of the Fund's portfolio will not always reflect the composition of the 50/50 Blended Benchmark.

Performance Table Closing [Text Block]

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The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

(Columbia Thermostat Fund B) | (Columbia Thermostat Fund) | Barclays U.S. Aggregate Bond Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

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1 Year

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7.84%

5 Years

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6.50%

Life of Fund

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5.33%

Inception Date

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Sep. 25, 2002

(Columbia Thermostat Fund B) | (Columbia Thermostat Fund) | 50-50 S&P 500/Barclays Capital Aggregate Bond (an equally weighted custom composite of the Fund's primary benchmarks for equity and debt securities, established by the Investment Manager; reflects no deductions for fees, expenses or taxes)

Risk/Return:

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1 Year

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5.28%

5 Years

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3.54%

Life of Fund

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6.43%

Inception Date

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Sep. 25, 2002

(Columbia Thermostat Fund B) | (Columbia Thermostat Fund) | Lipper Flexible Portfolio Funds Index (reflects no deductions for taxes)

Risk/Return:

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1 Year

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(1.16%)

5 Years

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2.02%

Life of Fund

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7.10%

Inception Date

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Sep. 25, 2002

(Columbia Thermostat Fund B) | (Columbia Thermostat Fund) | S&P 500® Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

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1 Year

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2.11%

5 Years

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(0.25%)

Life of Fund

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6.85%

Inception Date

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Sep. 25, 2002

(Columbia Thermostat Fund B) | (Columbia Thermostat Fund) | Class B Shares

Risk/Return:

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Maximum sales charge (load) imposed on purchases, as a % of offering price

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Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

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5.00%

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Management fees

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0.10%

Distribution and/or service (Rule 12b-1) fees

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0.75%

Other expenses

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0.52%

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Acquired Fund Fees and Expenses

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0.65%

Total annual Fund operating expenses

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2.02%

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Fee waivers and/or reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.37%)

^[9]

Total annual Fund operating expenses after fee waivers and/or reimbursements

rr_NetExpensesOverAssets

1.65%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

668

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

898

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,254

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,174

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

168

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

598

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

1,054

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

2,174

Annual Return 2003

rr_AnnualReturn2003

18.59%

Annual Return 2004

rr_AnnualReturn2004

8.27%

Annual Return 2005

rr_AnnualReturn2005

4.56%

Annual Return 2006

rr_AnnualReturn2006

9.91%

Annual Return 2007

rr_AnnualReturn2007

7.71%

Annual Return 2008

rr_AnnualReturn2008

(31.10%)

Annual Return 2009

rr_AnnualReturn2009

31.37%

Annual Return 2010

rr_AnnualReturn2010

16.64%

Annual Return 2011

rr_AnnualReturn2011

4.19%

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-date return as of March 31, 2012: 8.06%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

8.06%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

2nd quarter 2009:

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

19.07%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

4th quarter 2008:

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(19.47%)

1 Year

rr_AverageAnnualReturnYear01

(0.81%)

5 Years

rr_AverageAnnualReturnYear05

3.10%

Life of Fund

rr_AverageAnnualReturnSinceInception

6.65%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 25, 2002

(Columbia Thermostat Fund B) | (Columbia Thermostat Fund) | Class B Shares | returns after taxes on distributions

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(1.53%)

5 Years

rr_AverageAnnualReturnYear05

2.27%

Life of Fund

rr_AverageAnnualReturnSinceInception

5.70%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 25, 2002

(Columbia Thermostat Fund B) | (Columbia Thermostat Fund) | Class B Shares | returns after taxes on distributions and sale of Fund shares

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(0.53%)

5 Years

rr_AverageAnnualReturnYear05

2.24%

Life of Fund

rr_AverageAnnualReturnSinceInception

5.38%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 25, 2002

(Columbia Thermostat Fund Z) | (Columbia Thermostat Fund)

Risk/Return:

rr_RiskReturnAbstract

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation.

Expense [Heading]

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Fees and Expenses of the Fund

Expense Narrative [Text Block]

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This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

2013-04-30

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund will indirectly bear the expenses associated with portfolio turnover of the underlying Portfolio Funds in which the Fund invests. Each Portfolio Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A Portfolio Fund's higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when its shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 130% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

130.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class Z shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire on April 30, 2013, they are only reflected in the 1 year example and the first year of the 3, 5 and 10 year examples.

Based on the assumptions listed above, your costs would be:

Expense Example Closing [Text Block]

rr_ExpenseExampleClosingTextBlock

Remember this is an example only. Your actual costs may be higher or lower.

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund pursues its investment objective by investing in other mutual funds. As a "fund of funds," under normal circumstances, the Fund allocates at least 95% of its net assets (stock/bond assets) among a selected group of stock and bond mutual funds (Portfolio Funds) according to the current level of Standard & Poor's (S&P) 500® Index. Generally, when the S&P 500® Index goes up in relation to predetermined ranges set by Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), the Fund sells a portion of its stock funds and invests more in the bond funds and when the S&P 500® Index goes down in relation to the ranges, the Fund increases its investment in the stock funds. Under normal circumstances, the Fund may invest up to 5% of net assets plus any cash received that day in cash, high quality short-term paper and government securities.

Many asset allocation funds typically move assets from stocks to bonds when the market goes up, and from bonds to stocks when the market goes down. Most asset allocation funds are run by sophisticated investment professionals, who make subjective decisions based on economic and financial data and complex graphs of market behavior. By contrast, the day-to-day investment decisions for the Fund are made according to a single predetermined rule. The temperature in your house is run by a single rule: your thermostat turns on the furnace if your house is too cold or turns on the air conditioner if your house is too warm. This Fund works the same way, so it is named Columbia Thermostat Fund.

Because the Fund invests according to a pre-set program, there is no need for subjective day-to-day management. Although another successful asset allocation strategy might do better than the Fund, the Fund is designed for those who doubt the wisdom of trying to "time" the market and are unsure of the long-term trend of the stock market. The Fund takes psychology out of investing; it avoids the temptation to buy more stocks because the stock market is currently going up or to sell stocks because the market is declining. The Fund operates continuously and substantially automatically, subject to periodic review of the pre-set program by the Investment Manager and the Fund's Board of Trustees. As described more fully below, the Investment Manager has the authority to review the structure and allocation ranges of the stock/bond allocation table and to make any changes considered appropriate.

The Investment Manager chooses the Portfolio Funds to provide participation in the major sectors of the stock and bond markets. If you believe that the stock market will tend to go up most of the time, then you should probably own a fully invested stock fund and use a buy-and-hold strategy. Buy-and-hold was an excellent strategy in the 1982-1999 bull market. However, there have been long periods in the past when buy-and-hold was not the best strategy, such as 1930-1954 and 1969-1981, when the market fluctuated but did not make significant new highs. The Fund may be a good investment choice for you if you believe that the market may fluctuate in a trading range for many years, that a remarkable bull market ended early in 2000 and that the market may not reach significant new highs for many years.

The Fund invests its stock/bond assets among the Portfolio Funds according to an asset allocation table. The current allocation table is set forth below.

Stock/Bond Allocation Table

                                      How the Fund will Invest the Stock/Bond Assets

                                      ----------------------------------------------



Level of the S and P 500(R) Index   	    Stock Percentage     Bond Percentage

---------------------------------           ----------------     ---------------

over 1750                                          10%                90%

over 1700 -- 1750                                  15%                85%

over 1650 -- 1700                                  20%                80%

over 1600 -- 1650                                  25%                75%

over 1550 -- 1600                                  30%                70%

over 1500 -- 1550                                  35%                65%

over 1450 -- 1500                                  40%                60%

over 1400 -- 1450                                  45%                55%

over 1350 -- 1400                                  50%                50%

over 1300 -- 1350                                  55%                45%

over 1250 -- 1300                                  60%                40%

over 1200 -- 1250                                  65%                35%

over 1150 -- 1200                                  70%                30%

over 1100 -- 1150                                  75%                25%

over 1050 -- 1100                                  80%                20%

over 1000 -- 1050                                  85%                15%

1000 and under                                     90%                10%

When the S&P 500® Index moves into a new band on the table, the Fund promptly will rebalance the stock/bond mix to reflect the new S&P 500® Index price level by redeeming shares of some Portfolio Funds and purchasing shares of other Portfolio Funds. The only exception will be a "31-day Rule"; in order to reduce taxable events, after the Fund has increased its percentage allocation to either stock funds or bond funds, it will not decrease that allocation for at least 31 days. Following a change in the Fund's stock/bond mix, if the S&P 500® Index remains within the same band for a while, normal market fluctuations will change the values of the Fund's holdings of stock Portfolio Funds and bond Portfolio Funds. The Investment Manager will invest cash flows from sales (or redemptions) of Fund shares to bring the stock/bond mix back toward the allocation percentages for that S&P 500® Index band. For example, if the S&P 500® Index is in the 1150-1200 band, and the value of the holdings of the stock Portfolio Funds has dropped to 68% of the value of the holdings of all Portfolio Funds, the Investment Manager would invest new cash in the stock Portfolio Funds (or cash for redemptions would come from the bond Portfolio Funds). If the 31-day Rule is in effect, the Investment Manager will invest new cash at the stock/bond percentage allocation as of the latest rebalancing.

As an illustrative example, suppose the following:

 		              Level of the 		           How the Fund will invest

Date		          S and P 500(R) Index                       the Stock/Bond Assets

--------        ---------------------------------------         --------------------------------

Nov. 1             We begin when the market is 1380                  50% stocks, 50% bonds

Dec. 1             The S and P 500(R) goes to 1401              rebalance 45% stocks, 55% bonds

Dec. 6           The S and P 500(R) drops back to 1390              no reversal for 31 days

Jan. 2              The S and P 500(R) is at 1352               rebalance 50% stocks, 50% bonds

Jan. 20            The S and P 500(R) drops to 1349             rebalance 55% stocks, 45% bonds



      The market has made a continuation move by going through a second action level,

          not a reversal move, so the 31-day Rule does not apply in this case.



Jan. 30            The S and P 500(R) goes up to 1355               no reversal for 31 days

Feb. 20              The S and P 500(R) is at 1360              rebalance 50% stocks, 50% bonds

The following table shows the seven stock Portfolio Funds and three bond Portfolio Funds that the Fund currently uses in its "fund of funds" structure and the current allocation percentage for each Portfolio Fund within the stock or bond category. As described more fully below, the Investment Manager may substitute or add additional Portfolio Funds at any time, including funds introduced after the date of this prospectus. The allocation percentage within each stock/bond category is achieved by rebalancing the investments within the category whenever the S&P 500® Index moves into a new band on the allocation table, subject to the 31-day Rule described above. The Fund does not liquidate its investment in one Portfolio Fund in order to invest in another Portfolio Fund except in connection with a rebalancing due to a move of the S&P 500® Index into a new band (or due to a change by the Investment Manager in the stock/bond allocation table to the Portfolio Funds or to the relative allocation among them). Until a subsequent rebalancing, the Fund's investments in, and redemptions from, the stock Portfolio Funds or the bond Portfolio Funds are allocated among the Portfolio Funds in a manner that will reduce any deviation of the relative values of the Fund's holdings of the Funds from the allocation percentages shown below.

Allocation of Stock/Bond Assets Within Asset Classes

Stock Funds                                   Type of Fund 	             Allocation

-------------------------------------  ------------------------------------  -----------

Columbia Acorn Fund                    Small/Mid-cap growth                          15%

Columbia Acorn Select                  Mid-cap growth                                10%

Columbia Acorn International           Small/Mid-cap international growth            20%

Columbia Dividend Income Fund          Large-cap value                               20%

Columbia Large Cap Enhanced Core Fund  Large-cap blend                               10%

Columbia Contrarian Core Fund          Large-cap blend                               15%

Columbia Select Large Cap Growth Fund  Large-cap growth                              10%

Total                                                                               100%



Bond Funds                                    Type of Fund 	             Allocation

-------------------------------------  ------------------------------------  -----------

Columbia Intermediate Bond Fund        Intermediate-term bonds                       50%

Columbia Income Opportunities Fund     High-yield bonds                              30%

Columbia U.S. Treasury Index Fund      U.S. Treasury notes/bonds                     20%

Total                                                                               100%

The Investment Manager has the authority to review the Portfolio Funds and the relative stock/bond allocation percentages among them and to make any changes considered appropriate.

Each of the Portfolio Funds is currently managed by the Investment Manager or its affiliates. The Fund does not pay any sales load on its purchases of shares of the Portfolio Funds. On an annual basis, or on an "emergency" basis if necessary, the Investment Manager reviews the structure, allocation percentages and Portfolio Funds and makes any changes considered appropriate. The Investment Manager typically addresses the following questions:

• Should the stock/bond allocation table be revised (perhaps because the stock market has made a long-term move outside of the bands set forth above)?
• Should there be a change in the Portfolio Funds or should there be a change in the percentage allocations among the stock/bond funds (perhaps because of a change of portfolio managers, change of investment style, change in relative valuation or a reorganization of a Portfolio Fund)?

Any such changes by the Investment Manager are expected to be infrequent.

Risk [Heading]

rr_RiskHeading

Principal Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Allocation Risk – The Fund uses an asset allocation strategy in pursuit of its investment objective. There is a risk that the Fund's allocation among asset classes or investments will cause the Fund's shares to lose value or cause the Fund to underperform other funds with similar investment objectives, or that the investments themselves will not produce the returns expected.

• Investing in Other Funds Risk – The performance of the underlying fund(s) in which the Fund invests could be adversely affected if other entities that invest in the same underlying fund(s) make relatively large investments or redemptions in the underlying fund(s). In addition, because the expenses and costs of the underlying fund(s) are shared by investors in the underlying fund, redemptions by other investors in the underlying fund could result in decreased economies of scale and increased operating expenses for the underlying fund. The Fund, and its shareholders, indirectly bear a portion of the expenses of the underlying fund(s). These transactions might also result in higher brokerage, tax or other costs for the Fund. This risk may be particularly important when one investor owns a substantial portion of any underlying fund. In addition, the Investment Manager has the authority to change the underlying fund(s) in which the Fund invests or to change the percentage of the Fund's investments allocated to each underlying fund. If an underlying fund pays fees to the Investment Manager or its affiliates, such as advisory fees, this could result in the Investment Manager having a potential conflict of interest in selecting the underlying fund(s) in which the Fund invests or in determining the percentage of the Fund's investments allocated to each underlying fund. In addition, the underlying funds are themselves subject to Investment Strategy Risk.

The Fund is subject indirectly to the following risks of the Portfolio Funds:

• Market Risk – Market risk refers to the possibility that the market values of securities that a Portfolio Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Portfolio Fund. Accordingly, an investment in a Portfolio Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Portfolio Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Interest Rate Risk – Debt securities are subject to interest rate risk. In general, if prevailing interest rates rise, the values of debt securities will tend to fall, and if interest rates fall, the values of debt securities will tend to rise. Changes in the value of a debt security usually will not affect the amount of income a Portfolio Fund receives from it but may affect the value of the Portfolio Fund's shares. Interest rate risk is generally greater for debt securities with longer maturities/durations.

• Credit Risk – Credit risk applies to most debt securities, but is generally less of a factor for obligations backed by the "full faith and credit" of the U.S. Government. A Portfolio Fund could lose money if the issuer of a debt security owned by the Fund is unable or perceived to be unable to pay interest or repay principal when it becomes due. Various factors could affect the issuer's actual or perceived willingness or ability to make timely interest or principal payments, including changes in the issuer's financial condition or in general economic conditions. Debt securities backed by an issuer's taxing authority may be subject to legal limits on the issuer's power to increase taxes or otherwise to raise revenue, or may be dependent on legislative appropriation or government aid. Certain debt securities are backed only by revenues derived from a particular project or source, rather than by an issuer's taxing authority, and thus may have a greater risk of default.

• Low and Below Investment Grade Securities Risk – Debt securities with the lowest investment grade rating (e.g., BBB by Standard & Poor's, a division of the McGraw-Hill Companies, Inc. (S&P), or Fitch, Inc. (Fitch) or Baa by Moody's Investors Service, Inc. (Moody's)), or that are below investment grade (which are commonly referred to as "junk bonds") (e.g., BB or below by S&P or Fitch or Ba by Moody's) and unrated securities of comparable quality are more speculative than securities with higher ratings and may experience greater price fluctuations. These securities tend to be more sensitive to credit risk than higher-rated securities, particularly during a downturn in the economy, which is more likely to weaken the ability of the issuers to make principal and interest payments on these securities. These securities typically pay a premium – a higher interest rate or yield – because of the increased risk of loss, including default. These securities also are generally less liquid than higher-rated securities. The securities ratings provided by Moody's, S&P and Fitch are based on analyses by these ratings agencies of the credit quality of the securities and may not take into account every risk related to whether interest or principal will be timely repaid.

• Value Securities Risk – Value securities are securities of companies that may have experienced, for example, adverse business, industry or other developments or may be subject to special risks that have caused the securities to be out of favor and, in turn, potentially undervalued. The market value of a portfolio security may not meet the Investment Manager's future value assessment of that security, or may decline. There is also a risk that it may take longer than expected for the value of these investments to rise to the believed value. In addition, value securities, at times, may not perform as well as growth securities or the stock market in general, and may be out of favor with investors for varying periods of time.

• Growth Securities Risk – Because growth securities typically trade at a higher multiple of earnings than other types of securities, the market values of growth securities may be more sensitive to changes in current or expected earnings than the market values of other types of securities. In addition, growth securities, at times, may not perform as well as value securities or the stock market in general, and may be out of favor with investors for varying periods of time.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Portfolio Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Portfolio Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Index Risk – U.S. Treasury Index Fund's value will generally decline when the performance of its targeted index declines. Because U.S. Treasury Index Fund is designed to track an index before fees and expenses, U.S. Treasury Index Fund cannot purchase other securities that may help offset declines in its index. In addition, because U.S. Treasury Index Fund may not hold all issues included in its index, may not always be fully invested, and bears advisory, administrative and other expenses and transaction costs in trading securities, U.S. Treasury Index Fund's performance may fail to match the performance of its targeted index, after taking expenses into account. It is not possible to invest directly in an index.

• U.S. Government Obligations Risk – While U.S. Treasury obligations are backed by the "full faith and credit" of the U.S. Government, such securities are nonetheless subject to credit risk (i.e., the risk that the U.S. Government may be, or may be perceived to be, unable or unwilling to honor its financial obligations, such as making payments). Securities issued or guaranteed by federal agencies or authorities and U.S. Government-sponsored instrumentalities or enterprises may or may not be backed by the full faith and credit of the U.S. Government. For example, securities issued by the Federal Home Loan Mortgage Corporation, the Federal National Mortgage Association and the Federal Home Loan Banks are neither insured nor guaranteed by the U.S. Government. These securities may be supported by the ability to borrow from the U.S. Treasury or only by the credit of the issuing agency, authority, instrumentality or enterprise and, as a result, are subject to greater credit risk than securities issued or guaranteed by the U.S. Treasury. Securities guaranteed by the Federal Deposit Insurance Corporation under its Temporary Liquidity Guarantee Program (TLGP) are subject to certain risks, including whether such securities will continue to trade in line with recent experience in relation to treasury and government agency securities in terms of yield spread and the volatility of such spread, as well as uncertainty as to how such securities will trade in the secondary market and whether that market will be liquid or illiquid. The TLGP is subject to change. See ABOUT THE FUNDS' INVESTMENTS - U.S. Government and Related Obligations in the Statement of Additional Information for more information.

• Derivatives Risk – Derivatives are financial contracts whose values are, for example, based on (or "derived" from) traditional securities (such as a stock or bond), assets (such as a commodity like gold or a foreign currency), reference rates (such as LIBOR) or market indices (such as the S&P 500® Index). Derivatives involve special risks and may result in losses or may limit a Portfolio Fund's potential gain from favorable market movements. Derivative strategies often involve leverage, which may exaggerate a loss, potentially causing a Portfolio Fund to lose more money than it would have lost had it invested in the underlying security or other asset. The values of derivatives may move in unexpected ways, especially in unusual market conditions, and may result in increased volatility, among other consequences. The use of derivatives may also increase the amount of taxes payable by shareholders holding shares in a taxable account. Other risks arise from a Portfolio Fund's potential inability to terminate or to sell derivative positions. A liquid secondary market may not always exist for the Portfolio Fund's derivative positions at times when the Portfolio Fund might wish to terminate or to sell such positions. Over-the-counter instruments (investments not traded on an exchange) may be illiquid, and transactions in derivatives traded in the over-the-counter market are subject to the risk that the other party will not meet its obligations. The use of derivatives also involves the risks of mispricing or improper valuation and that changes in the value of the derivative may not correlate perfectly with the underlying security, asset, reference rate or index. A Portfolio Fund also may not be able to find a suitable derivative transaction counterparty, and thus may be unable to engage in derivative transactions when it is deemed favorable to do so, or at all. U.S. federal legislation has recently been enacted that provides for new clearing, margin, reporting and registration requirements for participants in the derivatives market. While the ultimate impact is not yet clear, these changes could restrict and/or impose significant costs or other burdens upon the Fund's participation in derivatives transactions. For more information on the risks of derivative investments and strategies, see the Statement of Additional Information.

• Convertible Securities Risk – Certain Portfolio Funds invest in convertible securities, which are subject to the usual risks associated with debt securities, such as interest rate risk and credit risk. Convertible securities also react to changes in the value of the common stock into which they convert. Because the value of a convertible security can be influenced by both interest rates and the common stock's market movements, a convertible security generally is not as sensitive to interest rates as a similar debt security, and generally will not vary in value in response to other factors to the same extent as the underlying common stock. In the event of a liquidation of the issuing company, holders of convertible securities would typically be paid before the company's common stockholders but after holders of any senior debt obligations of the company. A Portfolio Fund may be forced to convert a convertible security before it otherwise would choose to do so, which may decrease the Portfolio Fund's return.

• Non-Diversified Mutual Fund Risk – If a Portfolio Fund is non-diversified, that Portfolio Fund generally may invest a greater percentage of its total assets in the securities of fewer issuers than may a "diversified" fund. This increases the risk that a change in the value of any one investment held by the non-diversified Portfolio Fund could affect the overall value of the Portfolio Fund more than it would affect that of a diversified fund holding a greater number of investments. Accordingly, a non-diversified Portfolio Fund's value will likely be more volatile than the value of more diversified funds. A Portfolio Fund that is non-diversified may not operate as a non-diversified fund at all times.

• Technology Sector Risk – Companies in the technology sector are subject to significant competitive pressures, such as aggressive pricing of their products or services, new market entrants, competition for market share, short product cycles due to an accelerated rate of technological developments and the potential for limited earnings and/or falling profit margins. These companies also face the risks that new services, equipment or technologies will not be accepted by consumers and businesses or will become rapidly obsolete. These factors can affect the profitability of technology companies and, as a result, the value of their securities. Also, patent protection is integral to the success of many companies in the technology sector, and profitability can be affected materially by, among other things, the cost of obtaining (or failing to obtain) patent approvals, the cost of litigating patent infringement and the loss of patent protection for products (which significantly increases pricing pressures and can materially reduce profitability with respect to such products). In addition, many technology companies have limited operating histories. Prices of these companies' securities historically have been more volatile than other securities, especially over the short term. Because certain Portfolio Funds invest a significant portion of their net assets in the equity securities of technology companies, a Portfolio Fund's price may be more volatile than a fund that is invested in a more diverse range of market sectors.

• Health Care Sector Risk - Companies in the health care sector are subject to extensive government regulation. Their profitability can be affected significantly and adversely by restrictions on government reimbursement for medical expenses, government approval of medical products and services, competitive pricing pressures, an increased emphasis on outpatient and other alternative services and other factors. Patent protection is integral to the success of companies in the health care sector, and profitability can be affected materially by, among other things, the cost of obtaining (or failing to obtain) patent approvals, the cost of litigating patent infringement and the loss of patent protection for medical products (which significantly increases pricing pressures and can materially reduce profitability with respect to such products). Companies in the health care sector also potentially are subject to extensive product liability and other similar litigation. Companies in the health care sector are affected by the rising cost of medical products and services, and the effects of such rising costs can be particularly pronounced for companies that are dependent on a relatively limited number of products or services. Medical products also frequently become obsolete due to industry innovation or other causes. Because certain Portfolio Funds invest a significant portion of their net assets in the equity securities of health care companies, a Portfolio Fund's price may be more volatile than a fund that is invested in a more diverse range of market sectors.

Risk Nondiversified Status [Text]

rr_RiskNondiversifiedStatus

Non-Diversified Mutual Fund Risk – If a Portfolio Fund is non-diversified, that Portfolio Fund generally may invest a greater percentage of its total assets in the securities of fewer issuers than may a "diversified" fund. This increases the risk that a change in the value of any one investment held by the non-diversified Portfolio Fund could affect the overall value of the Portfolio Fund more than it would affect that of a diversified fund holding a greater number of investments. Accordingly, a non-diversified Portfolio Fund's value will likely be more volatile than the value of more diversified funds. A Portfolio Fund that is non-diversified may not operate as a non-diversified fund at all times.

Bar Chart and Performance Table [Heading]

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Performance Information

Performance Narrative [Text Block]

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The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

Performance Information Illustrates Variability of Returns [Text]

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The bar chart below shows you how the performance of the Fund's Class Z shares has varied from year to year.

Performance Availability Phone [Text]

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800.345.6611

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.columbiamanagement.com

Performance Past Does Not Indicate Future [Text]

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The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.

Bar Chart [Heading]

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Year by Year Total Return (%) as of December 31 Each Year

^[31]

Bar Chart Narrative [Text Block]

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The bar chart below shows you how the performance of the Fund's Class Z shares has varied from year to year.

Bar Chart Closing [Text Block]

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Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    19.33%

Worst:   4th quarter 2008:   -19.26%

Performance Table Heading

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Average Annual Total Return as of December 31, 2011

Performance Table Uses Highest Federal Rate

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The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.

Performance Table Not Relevant to Tax Deferred

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In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Performance Table Narrative

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The table compares the Fund's returns for each period with those of the S&P 500® Index, the Fund's primary benchmark for equity securities, the Barclays U.S. Aggregate Bond Index, the Fund's primary benchmark for debt securities, the Lipper Flexible Portfolio Funds Index and a 50/50 Blended Benchmark. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. The Barclays U.S. Aggregate Bond Index is a market value-weighted index that tracks the daily price, coupon, pay-downs, and total return performance of fixed-rate, publicly placed, dollar-denominated, and non-convertible investment grade debt issues with at least $250 million par amount outstanding and with at least one year to final maturity. The Lipper Flexible Portfolio Funds Index is an equal-weighted index of the 30 largest mutual funds within the Flexible Portfolio fund classification, as defined by Lipper, and shows how the Fund's performance compares with the returns of an index of funds with similar investment objectives. The 50/50 Blended Benchmark was established by the Investment Manager to show how the Fund's performance compares to an equally weighted custom composite of the Fund's primary equity and primary debt benchmarks, the S&P 500® Index and the Barclays U.S. Aggregate Bond Index, respectively. The percentage of the Fund's assets allocated to underlying stock and bond Portfolio Funds will vary, and accordingly the composition of the Fund's portfolio will not always reflect the composition of the 50/50 Blended Benchmark.

Performance Table Closing [Text Block]

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The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

(Columbia Thermostat Fund Z) | (Columbia Thermostat Fund) | Barclays U.S. Aggregate Bond Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

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1 Year

rr_AverageAnnualReturnYear01

7.84%

5 Years

rr_AverageAnnualReturnYear05

6.50%

Life of Fund

rr_AverageAnnualReturnSinceInception

5.33%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 25, 2002

(Columbia Thermostat Fund Z) | (Columbia Thermostat Fund) | 50-50 S&P 500/Barclays Capital Aggregate Bond (an equally weighted custom composite of the Fund's primary benchmarks for equity and debt securities, established by the Investment Manager; reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

5.28%

5 Years

rr_AverageAnnualReturnYear05

3.54%

Life of Fund

rr_AverageAnnualReturnSinceInception

6.43%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 25, 2002

(Columbia Thermostat Fund Z) | (Columbia Thermostat Fund) | Lipper Flexible Portfolio Funds Index (reflects no deductions for taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(1.16%)

5 Years

rr_AverageAnnualReturnYear05

2.02%

Life of Fund

rr_AverageAnnualReturnSinceInception

7.10%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 25, 2002

(Columbia Thermostat Fund Z) | (Columbia Thermostat Fund) | S&P 500® Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

2.11%

5 Years

rr_AverageAnnualReturnYear05

(0.25%)

Life of Fund

rr_AverageAnnualReturnSinceInception

6.85%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 25, 2002

(Columbia Thermostat Fund Z) | (Columbia Thermostat Fund) | Class Z Shares

Risk/Return:

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Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

none

Management fees

rr_ManagementFeesOverAssets

0.10%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.28%

^[4]

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.65%

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.03%

^[5]

Fee waivers and/or reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.13%)

^[9]

Total annual Fund operating expenses after fee waivers and/or reimbursements

rr_NetExpensesOverAssets

0.90%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

92

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

315

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

556

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,248

Annual Return 2003

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19.79%

Annual Return 2004

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9.17%

Annual Return 2005

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5.50%

Annual Return 2006

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10.86%

Annual Return 2007

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8.49%

Annual Return 2008

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(30.53%)

Annual Return 2009

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32.29%

Annual Return 2010

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17.58%

Annual Return 2011

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4.85%

Year to Date Return, Label

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Year-to-date return as of March 31, 2012: 8.29%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

8.29%

Highest Quarterly Return, Label

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2nd quarter 2009:

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

19.33%

Lowest Quarterly Return, Label

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4th quarter 2008:

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(19.26%)

1 Year

rr_AverageAnnualReturnYear01

4.85%

5 Years

rr_AverageAnnualReturnYear05

4.21%

Life of Fund

rr_AverageAnnualReturnSinceInception

7.51%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 25, 2002

(Columbia Thermostat Fund Z) | (Columbia Thermostat Fund) | Class Z Shares | returns after taxes on distributions

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

3.80%

5 Years

rr_AverageAnnualReturnYear05

3.12%

Life of Fund

rr_AverageAnnualReturnSinceInception

6.26%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 25, 2002

(Columbia Thermostat Fund Z) | (Columbia Thermostat Fund) | Class Z Shares | returns after taxes on distributions and sale of Fund shares

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

3.15%

5 Years

rr_AverageAnnualReturnYear05

3.06%

Life of Fund

rr_AverageAnnualReturnSinceInception

5.97%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 25, 2002

(Columbia Acorn European Fund A,C & I) | (Columbia Acorn European Fund)

Risk/Return:

rr_RiskReturnAbstract

Objective [Heading]

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Investment Objective

Objective, Primary [Text Block]

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The Fund seeks long-term capital appreciation.

Expense [Heading]

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Fees and Expenses of the Fund

Expense Narrative [Text Block]

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This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds. More information about these and other discounts is available from your financial advisor, in the Choosing a Share Class section beginning on page 18 of this prospectus and in Appendix D to the Statement of Additional Information under Sales Charge Waivers beginning on page D-1.

Shareholder Fees Caption [Text]

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Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

2013-04-30

Portfolio Turnover [Heading]

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Portfolio Turnover

Portfolio Turnover [Text Block]

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The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 17% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

17.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expense Example [Heading]

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Example

Expense Example Narrative [Text Block]

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The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class A, Class C or Class I shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire on April 30, 2013, they are only reflected in the 1 year example and the first year of the 3 year example.

Based on the assumptions listed above, your costs would be:

Expense Example Closing [Text Block]

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Remember this is an example only. Your actual costs may be higher or lower.

Strategy [Heading]

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Principal Investment Strategies

Strategy Narrative [Text Block]

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Under normal circumstances, the Fund invests at least 80% of its net assets (plus any borrowing for investment purposes) in European companies. Under normal circumstances, the Fund invests at least 70% of its total assets in companies in Western European countries (for example, the United Kingdom, Germany, France and Italy), but also may invest up to 30% of its total assets in companies in emerging Central and Eastern European countries (for example, Poland, the Czech Republic, Turkey and Cyprus), including up to 10% of its total assets in companies in Russia and the Ukraine. For purposes of the Fund's policies, the Fund may invest in a company if (i) it is domiciled in, or the principal trading market for its securities is in, a European country, (ii) it derives 50% or more of its economic value from goods produced, sales made or services performed or has at least 50% of its assets in a European country or (iii) it is a holding company that predominantly holds shares in such companies. The Fund may invest in a variety of countries, industries and sectors and does not attempt to invest a specific percentage of its assets in any given country, industry or sector.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to initially invest in a limited number of companies (generally under 100), offering the potential to provide above-average growth over time.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Risk [Heading]

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Principal Risks

Risk Narrative [Text Block]

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• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Currency Risk – Securities denominated in non-U.S. dollar currencies are subject to the risk that, for example, if the value of a foreign currency were to decline against the U.S. dollar, such decline would reduce the U.S. dollar value of any securities held by the Fund denominated in that currency.

• Special Situations Risk – Securities of companies that are involved in an initial public offering or a major corporate event, such as a business consolidation or restructuring, which may present special risk because of the high degree of uncertainty that can be associated with such events. Securities issued in initial public offerings often are issued by companies that are in the early stages of development, have a history of little or no revenues and may operate at a loss following the offering. It is possible that there will be no active trading market for the securities after the offering, and that the market price of the securities may be subject to significant and unpredictable fluctuations. Investing in special situations may have a magnified effect on the performance of funds with small amounts of assets.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Performance Information

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

Because the Fund commenced investment operations on August 19, 2011, no year-by-year total return bar chart or average annual total return table is being presented. The year-by year-total return bar chart and the average annual total return table will be provided after the Fund has annual returns for at least one calendar year.

Recent performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800.345.6611

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.columbiamanagement.com

(Columbia Acorn European Fund A,C & I) | (Columbia Acorn European Fund) | Class A Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[1]

Management fees

rr_ManagementFeesOverAssets

1.19%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

18.29%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

19.73%

Fee waivers and/or reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(17.98%)

^[10]

Total annual Fund operating expenses after fee waivers and/or reimbursements

rr_NetExpensesOverAssets

1.75%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

743

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

4,038

(Columbia Acorn European Fund A,C & I) | (Columbia Acorn European Fund) | Class C Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[2]

Management fees

rr_ManagementFeesOverAssets

1.19%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other expenses

rr_OtherExpensesOverAssets

19.93%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

22.12%

Fee waivers and/or reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(19.62%)

^[10]

Total annual Fund operating expenses after fee waivers and/or reimbursements

rr_NetExpensesOverAssets

2.50%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

353

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

4,045

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

253

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

4,045

(Columbia Acorn European Fund A,C & I) | (Columbia Acorn European Fund) | Class I Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

Management fees

rr_ManagementFeesOverAssets

1.19%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

17.78%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

18.97%

Fee waivers and/or reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(17.66%)

^[10]

Total annual Fund operating expenses after fee waivers and/or reimbursements

rr_NetExpensesOverAssets

1.31%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

133

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

3,537

(Columbia Acorn European Fund Z) | (Columbia Acorn European Fund)

Risk/Return:

rr_RiskReturnAbstract

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation.

Expense [Heading]

rr_ExpenseHeading

Fees and Expenses of the Fund

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

2013-04-30

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 17% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

17.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class Z shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire on April 30, 2013, they are only reflected in the 1 year example and the first year of the 3 year example.

Based on the assumptions listed above, your costs would be:

Expense Example Closing [Text Block]

rr_ExpenseExampleClosingTextBlock

Remember this is an example only. Your actual costs may be higher or lower.

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 80% of its net assets (plus any borrowing for investment purposes) in European companies. Under normal circumstances, the Fund invests at least 70% of its total assets in companies in Western European countries (for example, the United Kingdom, Germany, France and Italy), but also may invest up to 30% of its total assets in companies in emerging Central and Eastern European countries (for example, Poland, the Czech Republic, Turkey and Cyprus), including up to 10% of its total assets in companies in Russia and the Ukraine. For purposes of the Fund's policies, the Fund may invest in a company if (i) it is domiciled in, or the principal trading market for its securities is in, a European country, (ii) it derives 50% or more of its economic value from goods produced, sales made or services performed or has at least 50% of its assets in a European country or (iii) it is a holding company that predominantly holds shares in such companies. The Fund may invest in a variety of countries, industries and sectors and does not attempt to invest a specific percentage of its assets in any given country, industry or sector.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to initially invest in a limited number of companies (generally under 100), offering the potential to provide above-average growth over time.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Risk [Heading]

rr_RiskHeading

Principal Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Currency Risk – Securities denominated in non-U.S. dollar currencies are subject to the risk that, for example, if the value of a foreign currency were to decline against the U.S. dollar, such decline would reduce the U.S. dollar value of any securities held by the Fund denominated in that currency.

• Special Situations Risk – Securities of companies that are involved in an initial public offering or a major corporate event, such as a business consolidation or restructuring, which may present special risk because of the high degree of uncertainty that can be associated with such events. Securities issued in initial public offerings often are issued by companies that are in the early stages of development, have a history of little or no revenues and may operate at a loss following the offering. It is possible that there will be no active trading market for the securities after the offering, and that the market price of the securities may be subject to significant and unpredictable fluctuations. Investing in special situations may have a magnified effect on the performance of funds with small amounts of assets.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Performance Information

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

Because the Fund commenced investment operations on August 19, 2011, no year-by-year total return bar chart or average annual total return table is being presented. The year-by year-total return bar chart and the average annual total return table will be provided after the Fund has annual returns for at least one calendar year.

Recent performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800.345.6611

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.columbiamanagement.com

(Columbia Acorn European Fund Z) | (Columbia Acorn European Fund) | Class Z Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

none

Management fees

rr_ManagementFeesOverAssets

1.19%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

17.83%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

19.02%

Fee waivers and/or reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(17.52%)

^[11]

Total annual Fund operating expenses after fee waivers and/or reimbursements

rr_NetExpensesOverAssets

1.50%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

153

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

3,557

(Columbia Acorn Emerging Markets Fund A,C & I) | (Columbia Acorn Emerging Markets Fund)

Risk/Return:

rr_RiskReturnAbstract

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation.

Expense [Heading]

rr_ExpenseHeading

Fees and Expenses of the Fund

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds. More information about these and other discounts is available from your financial advisor, in the Choosing a Share Class section beginning on page 18 of this prospectus and in Appendix D to the Statement of Additional Information under Sales Charge Waivers beginning on page D-1.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

2013-04-30

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 9% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

9.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class A, Class C or Class I shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire on April 30, 2013, they are only reflected in the 1 year example and the first year of the 3 year example.

Based on the assumptions listed above, your costs would be:

Expense Example Closing [Text Block]

rr_ExpenseExampleClosingTextBlock

Remember this is an example only. Your actual costs may be higher or lower.

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 80% of its net assets (plus any borrowing for investment purposes) in companies located in emerging market countries, including frontier market countries. Emerging market countries are those countries whose economies are developing or emerging from underdevelopment (for example, China, India, Poland and Turkey). Frontier market countries generally have smaller economies and even less developed capital markets than traditional emerging market countries (for example, Vietnam, Colombia, Nigeria and Kazakhstan). For purposes of the Fund's policies, the Fund may invest in a company if (i) it is domiciled in, or the principal trading market for its securities is in, an emerging market country, (ii) it derives 50% or more of its economic value from goods produced, sales made or services performed or has at least 50% of its assets in an emerging market country or countries or (iii) it is a holding company that predominantly holds shares in such companies. The Fund may invest in a variety of countries, industries and sectors and does not attempt to invest a specific percentage of its assets in any given country, industry or sector.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion. Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to initially invest in a limited number of companies (generally under 100), offering the potential to provide above-average growth over time.

Generally, the Investment Manager will determine which countries are emerging market countries by reference to the countries included in the S&P Emerging Markets Broad Market Index (BMI), and will determine which countries are frontier market countries by reference to the countries included in the S&P Frontier BMI. In addition, the Fund may invest in certain developing market countries that are not included in either the S&P Emerging Markets BMI or the S&P Frontier BMI (for example, Serbia and Senegal), but which are included on another independent third-party listing of emerging market and/or frontier market countries. The Investment Manager will make all determinations as to whether a company is an emerging market company at the time of investment. The countries that comprise emerging market countries, including frontier market countries, may change from time to time.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Risk [Heading]

rr_RiskHeading

Principal Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Frontier Market Risk — Frontier market countries generally have smaller economies and even less developed capital markets than traditional emerging market countries and, as a result, the risks of investing in emerging market countries are magnified in frontier market countries. The magnification of risks are the result of: potential for extreme price volatility and illiquidity in frontier market countries; government ownership or control of parts of private sector and of certain companies; trade barriers, exchange controls, managed adjustments in relative currency values and other protectionist measures imposed or negotiated by the countries with which frontier market countries trade; and the relatively new and unsettled securities laws in many frontier market countries.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Currency Risk – Securities denominated in non-U.S. dollar currencies are subject to the risk that, for example, if the value of a foreign currency were to decline against the U.S. dollar, such decline would reduce the U.S. dollar value of any securities held by the Fund denominated in that currency.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Special Situations Risk – Securities of companies that are involved in an initial public offering or a major corporate event, such as a business consolidation or restructuring, which may present special risk because of the high degree of uncertainty that can be associated with such events. Securities issued in initial public offerings often are issued by companies that are in the early stages of development, have a history of little or no revenues and may operate at a loss following the offering. It is possible that there will be no active trading market for the securities after the offering, and that the market price of the securities may be subject to significant and unpredictable fluctuations. Investing in special situations may have a magnified effect on the performance of funds with small amounts of assets.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Performance Information

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

Because the Fund commenced investment operations on August 19, 2011, no year-by-year total return bar chart or average annual total return table is being presented. The year-by year-total return bar chart and the average annual total return table will be provided after the Fund has annual returns for at least one calendar year.

Recent performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800.345.6611

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.columbiamanagement.com

(Columbia Acorn Emerging Markets Fund A,C & I) | (Columbia Acorn Emerging Markets Fund) | Class A Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[1]

Management fees

rr_ManagementFeesOverAssets

1.25%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

12.72%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

14.22%

^[6]

Fee waivers and/or reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(12.37%)

^[12]

Total annual Fund operating expenses after fee waivers and/or reimbursements

rr_NetExpensesOverAssets

1.85%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

752

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

3,268

(Columbia Acorn Emerging Markets Fund A,C & I) | (Columbia Acorn Emerging Markets Fund) | Class C Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[2]

Management fees

rr_ManagementFeesOverAssets

1.25%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other expenses

rr_OtherExpensesOverAssets

13.09%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

15.34%

^[6]

Fee waivers and/or reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(12.74%)

^[12]

Total annual Fund operating expenses after fee waivers and/or reimbursements

rr_NetExpensesOverAssets

2.60%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

363

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

3,088

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

263

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

3,088

(Columbia Acorn Emerging Markets Fund A,C & I) | (Columbia Acorn Emerging Markets Fund) | Class I Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

Management fees

rr_ManagementFeesOverAssets

1.25%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

12.05%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

13.30%

^[6]

Fee waivers and/or reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(11.89%)

^[12]

Total annual Fund operating expenses after fee waivers and/or reimbursements

rr_NetExpensesOverAssets

1.41%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

144

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

2,675

(Columbia Acorn Emerging Markets Fund Z) | (Columbia Acorn Emerging Markets Fund)

Risk/Return:

rr_RiskReturnAbstract

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation.

Expense [Heading]

rr_ExpenseHeading

Fees and Expenses of the Fund

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

2013-04-30

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 9% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

9.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class Z shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire on April 30, 2013, they are only reflected in the 1 year example and the first year of the 3 year example.

Based on the assumptions listed above, your costs would be:

Expense Example Closing [Text Block]

rr_ExpenseExampleClosingTextBlock

Remember this is an example only. Your actual costs may be higher or lower.

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 80% of its net assets (plus any borrowing for investment purposes) in companies located in emerging market countries, including frontier market countries. Emerging market countries are those countries whose economies are developing or emerging from underdevelopment (for example, China, India, Poland and Turkey). Frontier market countries generally have smaller economies and even less developed capital markets than traditional emerging market countries (for example, Vietnam, Colombia, Nigeria and Kazakhstan). For purposes of the Fund's policies, the Fund may invest in a company if (i) it is domiciled in, or the principal trading market for its securities is in, an emerging market country, (ii) it derives 50% or more of its economic value from goods produced, sales made or services performed or has at least 50% of its assets in an emerging market country or countries or (iii) it is a holding company that predominantly holds shares in such companies. The Fund may invest in a variety of countries, industries and sectors and does not attempt to invest a specific percentage of its assets in any given country, industry or sector.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion. Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to initially invest in a limited number of companies (generally under 100), offering the potential to provide above-average growth over time.

Generally, the Investment Manager will determine which countries are emerging market countries by reference to the countries included in the S&P Emerging Markets Broad Market Index (BMI), and will determine which countries are frontier market countries by reference to the countries included in the S&P Frontier BMI. In addition, the Fund may invest in certain developing market countries that are not included in either the S&P Emerging Markets BMI or the S&P Frontier BMI (for example, Serbia and Senegal), but which are included on another independent third-party listing of emerging market and/or frontier market countries. The Investment Manager will make all determinations as to whether a company is an emerging market company at the time of investment. The countries that comprise emerging market countries, including frontier market countries, may change from time to time.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Risk [Heading]

rr_RiskHeading

Principal Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Frontier Market Risk — Frontier market countries generally have smaller economies and even less developed capital markets than traditional emerging market countries and, as a result, the risks of investing in emerging market countries are magnified in frontier market countries. The magnification of risks are the result of: potential for extreme price volatility and illiquidity in frontier market countries; government ownership or control of parts of private sector and of certain companies; trade barriers, exchange controls, managed adjustments in relative currency values and other protectionist measures imposed or negotiated by the countries with which frontier market countries trade; and the relatively new and unsettled securities laws in many frontier market countries.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Currency Risk – Securities denominated in non-U.S. dollar currencies are subject to the risk that, for example, if the value of a foreign currency were to decline against the U.S. dollar, such decline would reduce the U.S. dollar value of any securities held by the Fund denominated in that currency.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Special Situations Risk – Securities of companies that are involved in an initial public offering or a major corporate event, such as a business consolidation or restructuring, which may present special risk because of the high degree of uncertainty that can be associated with such events. Securities issued in initial public offerings often are issued by companies that are in the early stages of development, have a history of little or no revenues and may operate at a loss following the offering. It is possible that there will be no active trading market for the securities after the offering, and that the market price of the securities may be subject to significant and unpredictable fluctuations. Investing in special situations may have a magnified effect on the performance of funds with small amounts of assets.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Performance Information

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

Because the Fund commenced investment operations on August 19, 2011, no year-by-year total return bar chart or average annual total return table is being presented. The year-by year-total return bar chart and the average annual total return table will be provided after the Fund has annual returns for at least one calendar year.

Recent performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800.345.6611

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.columbiamanagement.com

(Columbia Acorn Emerging Markets Fund Z) | (Columbia Acorn Emerging Markets Fund) | Class Z Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases, as a % of offering price

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value

rr_MaximumDeferredSalesChargeOverOther

none

Management fees

rr_ManagementFeesOverAssets

1.25%

Distribution and/or service (Rule 12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

12.10%

^[4]

Total annual Fund operating expenses

rr_ExpensesOverAssets

13.35%

^[6]

Fee waivers and/or reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(11.75%)

^[13]

Total annual Fund operating expenses after fee waivers and/or reimbursements

rr_NetExpensesOverAssets

1.60%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

163

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

2,698

[1] Contingent deferred sales charges (CDSC) on certain investments of between $1 million and $50 million redeemed within 18 months of purchase, charged as follows: 1.00% CDSC if redeemed within 12 months of purchase, and 0.50% CDSC if redeemed more than 12, but less than 18, months of purchase, with certain limited exceptions.

[2] This charge applies to investors who buy Class C shares and redeem them within one year of purchase, with certain limited exceptions.

[3] This charge decreases over time. See About Class B Shares - Sales Charges and Commissions for details.

[4] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[5] Total annual Fund operating expenses include the annualized average weighted fees and expenses of acquired funds (underlying Portfolio Funds). As a result, the amount shown is higher than the ratio of expenses to average net assets included in Financial Highlights, which reflects only those expenses paid directly by the Fund.

[6] During its initial fiscal period, the Fund had acquired fund fees and expenses of 0.04% on an annualized basis. Based on assumptions as to the Fund's expected investments in other investment companies during the current fiscal year, acquired fund fees and expenses are expected to be less than 0.01%.

[7] Columbia Management Investment Services Corp., the Fund's transfer agent, has contractually agreed, through August 14, 2013, to waive a portion of total annual Fund operating expenses attributable to transfer agency fees incurred by Class A shares and Class C shares. Pursuant to this agreement, total annual Fund operating expenses will be reduced by 0.04% for Class A shares and 0.02% for Class C shares.

[8] Columbia Management Investment Services Corp., the Fund's transfer agent, has contractually agreed, through August 14, 2013, to waive a portion of total annual Fund operating expenses attributable to transfer agency fees incurred by Class B shares. Pursuant to this agreement, total annual Fund operating expenses will be reduced by 0.03% for Class B shares.

[9] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that ordinary operating expenses (excluding distribution and service fees, interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies) do not exceed the annual rate of 0.25% of the Fund's average daily net assets, through April 30, 2013. The figure shown here is the amount of expected waivers and/or reimbursements. This fee and expense arrangement may only be modified or amended with approval from all parties to such arrangement, including the Fund and the Investment Manager.

[10] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that the ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) do not exceed the annual rates of 1.75%, 2.50% and 1.31% of the Fund's average daily net assets attributable to Class A, Class C and Class I shares, respectively, through April 30, 2013. The Investment Manager may recoup any fees waived and/or expenses reimbursed with respect to any share class of the Fund for a one-year period following the date of such fee waiver and/or reimbursement if such recovery does not cause the Fund's ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) to exceed the annual rates set forth in this prospectus, or to exceed such annual rate as may be in place at the time of the recoupment, whichever is less. This expense arrangement may only be modified or amended with approval from all parties to such arrangements, including the Fund and the Investment Manager.

[11] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that the ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) do not exceed the annual rate of 1.50% of the Fund's average daily net assets attributable to Class Z shares, through April 30, 2013. The Investment Manager may recoup any fees waived and/or expenses reimbursed with respect to any share class of the Fund for a one-year period following the date of such fee waiver and/or reimbursement if such recovery does not cause the Fund's ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) to exceed the annual rates set forth in this prospectus, or to exceed such annual rate as may be in place at the time of the recoupment, whichever is less. This expense arrangement may only be modified or amended with approval from all parties to such arrangements, including the Fund and the Investment Manager.

[12] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that the ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) do not exceed the annual rates of 1.85%, 2.60% and 1.41% of the Fund's average daily net assets attributable to Class A, Class C and Class I shares, respectively, through April 30, 2013. The Investment Manager may recoup any fees waived and/or expenses reimbursed with respect to any share class of the Fund for a one-year period following the date of such fee waiver and/or reimbursement if such recovery does not cause the Fund's ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) to exceed the annual rates set forth in this prospectus, or to exceed such annual rate as may be in place at the time of the recoupment, whichever is less. This expense arrangement may only be modified or amended with approval from all parties to such arrangements, including the Fund and the Investment Manager.

[13] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that the ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) do not exceed the annual rate of 1.60% of the Fund's average daily net assets attributable to Class Z shares, through April 30, 2013. The Investment Manager may recoup any fees waived and/or expenses reimbursed with respect to any share class of the Fund for a one-year period following the date of such fee waiver and/or reimbursement if such recovery does not cause the Fund's ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) to exceed the annual rates set forth in this prospectus, or to exceed such annual rate as may be in place at the time of the recoupment, whichever is less. This expense arrangement may only be modified or amended with approval from all parties to such arrangements, including the Fund and the Investment Manager.

[14] Year-to-date return as of March 31, 2012: 15.43%

[15] Year-to-date return as of March 31, 2012: 15.25%

[16] Year-to-date return as of March 31, 2012: 15.49%

[17] Year-to-date return as of March 31, 2012: 14.99%

[18] Year-to-date return as of March 31, 2012: 14.77%

[19] Year-to-date return as of March 31, 2012: 15.07%

[20] Year-to-date return as of March 31, 2012: 16.27%

[21] Year-to-date return as of March 31, 2012: 16.06%

[22] Year-to-date return as of March 31, 2012: 16.38%

[23] Year-to-date return as of March 31, 2012: 17.65%

[24] Year-to-date return as of March 31, 2012: 17.48%

[25] Year-to-date return as of March 31, 2012: 17.70%

[26] Year-to-date return as of March 31, 2012: 11.29%

[27] Year-to-date return as of March 31, 2012: 11.13%

[28] Year-to-date return as of March 31, 2012: 11.37%

[29] Year-to-date return as of March 31, 2012: 8.19%

[30] Year-to-date return as of March 31, 2012: 8.06%

[31] Year-to-date return as of March 31, 2012: 8.29%

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(Columbia Acorn Emerging Markets Fund Z) | (Columbia Acorn Emerging Markets Fund)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn Emerging Markets Fund)	Class Z Shares (Columbia Acorn Emerging Markets Fund Z)
Maximum sales charge (load) imposed on purchases, as a % of offering price	none
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn Emerging Markets Fund)		Class Z Shares (Columbia Acorn Emerging Markets Fund Z)
Management fees		1.25%
Distribution and/or service (Rule 12b-1) fees		none
Other expenses	[1]	12.10%
Total annual Fund operating expenses	[2]	13.35%
Fee waivers and/or reimbursements	[3]	(11.75%)
Total annual Fund operating expenses after fee waivers and/or reimbursements		1.60%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class Z shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire on April 30, 2013, they are only reflected in the 1 year example and the first year of the 3 year example.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn Emerging Markets Fund) (USD $)	1 Year	3 Years
Class Z Shares (Columbia Acorn Emerging Markets Fund Z)	163	2,698

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 9% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 80% of its net assets (plus any borrowing for investment purposes) in companies located in emerging market countries, including frontier market countries. Emerging market countries are those countries whose economies are developing or emerging from underdevelopment (for example, China, India, Poland and Turkey). Frontier market countries generally have smaller economies and even less developed capital markets than traditional emerging market countries (for example, Vietnam, Colombia, Nigeria and Kazakhstan). For purposes of the Fund's policies, the Fund may invest in a company if (i) it is domiciled in, or the principal trading market for its securities is in, an emerging market country, (ii) it derives 50% or more of its economic value from goods produced, sales made or services performed or has at least 50% of its assets in an emerging market country or countries or (iii) it is a holding company that predominantly holds shares in such companies. The Fund may invest in a variety of countries, industries and sectors and does not attempt to invest a specific percentage of its assets in any given country, industry or sector.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion. Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to initially invest in a limited number of companies (generally under 100), offering the potential to provide above-average growth over time.

Generally, the Investment Manager will determine which countries are emerging market countries by reference to the countries included in the S&P Emerging Markets Broad Market Index (BMI), and will determine which countries are frontier market countries by reference to the countries included in the S&P Frontier BMI. In addition, the Fund may invest in certain developing market countries that are not included in either the S&P Emerging Markets BMI or the S&P Frontier BMI (for example, Serbia and Senegal), but which are included on another independent third-party listing of emerging market and/or frontier market countries. The Investment Manager will make all determinations as to whether a company is an emerging market company at the time of investment. The countries that comprise emerging market countries, including frontier market countries, may change from time to time.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Frontier Market Risk — Frontier market countries generally have smaller economies and even less developed capital markets than traditional emerging market countries and, as a result, the risks of investing in emerging market countries are magnified in frontier market countries. The magnification of risks are the result of: potential for extreme price volatility and illiquidity in frontier market countries; government ownership or control of parts of private sector and of certain companies; trade barriers, exchange controls, managed adjustments in relative currency values and other protectionist measures imposed or negotiated by the countries with which frontier market countries trade; and the relatively new and unsettled securities laws in many frontier market countries.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Currency Risk – Securities denominated in non-U.S. dollar currencies are subject to the risk that, for example, if the value of a foreign currency were to decline against the U.S. dollar, such decline would reduce the U.S. dollar value of any securities held by the Fund denominated in that currency.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Special Situations Risk – Securities of companies that are involved in an initial public offering or a major corporate event, such as a business consolidation or restructuring, which may present special risk because of the high degree of uncertainty that can be associated with such events. Securities issued in initial public offerings often are issued by companies that are in the early stages of development, have a history of little or no revenues and may operate at a loss following the offering. It is possible that there will be no active trading market for the securities after the offering, and that the market price of the securities may be subject to significant and unpredictable fluctuations. Investing in special situations may have a magnified effect on the performance of funds with small amounts of assets.

Performance Information

Because the Fund commenced investment operations on August 19, 2011, no year-by-year total return bar chart or average annual total return table is being presented. The year-by year-total return bar chart and the average annual total return table will be provided after the Fund has annual returns for at least one calendar year.

Recent performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[2] During its initial fiscal period, the Fund had acquired fund fees and expenses of 0.04% on an annualized basis. Based on assumptions as to the Fund's expected investments in other investment companies during the current fiscal year, acquired fund fees and expenses are expected to be less than 0.01%.

[3] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that the ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) do not exceed the annual rate of 1.60% of the Fund's average daily net assets attributable to Class Z shares, through April 30, 2013. The Investment Manager may recoup any fees waived and/or expenses reimbursed with respect to any share class of the Fund for a one-year period following the date of such fee waiver and/or reimbursement if such recovery does not cause the Fund's ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) to exceed the annual rates set forth in this prospectus, or to exceed such annual rate as may be in place at the time of the recoupment, whichever is less. This expense arrangement may only be modified or amended with approval from all parties to such arrangements, including the Fund and the Investment Manager.

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(Columbia Thermostat Fund Z) | (Columbia Thermostat Fund)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Thermostat Fund)	Class Z Shares (Columbia Thermostat Fund Z)
Maximum sales charge (load) imposed on purchases, as a % of offering price	none
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Thermostat Fund)		Class Z Shares (Columbia Thermostat Fund Z)
Management fees		0.10%
Distribution and/or service (Rule 12b-1) fees		none
Other expenses	[1]	0.28%
Acquired Fund Fees and Expenses		0.65%
Total annual Fund operating expenses	[2]	1.03%
Fee waivers and/or reimbursements	[3]	(0.13%)
Total annual Fund operating expenses after fee waivers and/or reimbursements		0.90%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class Z shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire on April 30, 2013, they are only reflected in the 1 year example and the first year of the 3, 5 and 10 year examples.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Thermostat Fund) (USD $)	1 Year	3 Years	5 Years	10 Years
Class Z Shares (Columbia Thermostat Fund Z)	92	315	556	1,248

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund will indirectly bear the expenses associated with portfolio turnover of the underlying Portfolio Funds in which the Fund invests. Each Portfolio Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A Portfolio Fund's higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when its shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 130% of the average value of its portfolio.

Principal Investment Strategies

The Fund pursues its investment objective by investing in other mutual funds. As a "fund of funds," under normal circumstances, the Fund allocates at least 95% of its net assets (stock/bond assets) among a selected group of stock and bond mutual funds (Portfolio Funds) according to the current level of Standard & Poor's (S&P) 500® Index. Generally, when the S&P 500® Index goes up in relation to predetermined ranges set by Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), the Fund sells a portion of its stock funds and invests more in the bond funds and when the S&P 500® Index goes down in relation to the ranges, the Fund increases its investment in the stock funds. Under normal circumstances, the Fund may invest up to 5% of net assets plus any cash received that day in cash, high quality short-term paper and government securities.

Many asset allocation funds typically move assets from stocks to bonds when the market goes up, and from bonds to stocks when the market goes down. Most asset allocation funds are run by sophisticated investment professionals, who make subjective decisions based on economic and financial data and complex graphs of market behavior. By contrast, the day-to-day investment decisions for the Fund are made according to a single predetermined rule. The temperature in your house is run by a single rule: your thermostat turns on the furnace if your house is too cold or turns on the air conditioner if your house is too warm. This Fund works the same way, so it is named Columbia Thermostat Fund.

Because the Fund invests according to a pre-set program, there is no need for subjective day-to-day management. Although another successful asset allocation strategy might do better than the Fund, the Fund is designed for those who doubt the wisdom of trying to "time" the market and are unsure of the long-term trend of the stock market. The Fund takes psychology out of investing; it avoids the temptation to buy more stocks because the stock market is currently going up or to sell stocks because the market is declining. The Fund operates continuously and substantially automatically, subject to periodic review of the pre-set program by the Investment Manager and the Fund's Board of Trustees. As described more fully below, the Investment Manager has the authority to review the structure and allocation ranges of the stock/bond allocation table and to make any changes considered appropriate.

The Investment Manager chooses the Portfolio Funds to provide participation in the major sectors of the stock and bond markets. If you believe that the stock market will tend to go up most of the time, then you should probably own a fully invested stock fund and use a buy-and-hold strategy. Buy-and-hold was an excellent strategy in the 1982-1999 bull market. However, there have been long periods in the past when buy-and-hold was not the best strategy, such as 1930-1954 and 1969-1981, when the market fluctuated but did not make significant new highs. The Fund may be a good investment choice for you if you believe that the market may fluctuate in a trading range for many years, that a remarkable bull market ended early in 2000 and that the market may not reach significant new highs for many years.

The Fund invests its stock/bond assets among the Portfolio Funds according to an asset allocation table. The current allocation table is set forth below.

Stock/Bond Allocation Table

                                      How the Fund will Invest the Stock/Bond Assets

                                      ----------------------------------------------



Level of the S and P 500(R) Index   	    Stock Percentage     Bond Percentage

---------------------------------           ----------------     ---------------

over 1750                                          10%                90%

over 1700 -- 1750                                  15%                85%

over 1650 -- 1700                                  20%                80%

over 1600 -- 1650                                  25%                75%

over 1550 -- 1600                                  30%                70%

over 1500 -- 1550                                  35%                65%

over 1450 -- 1500                                  40%                60%

over 1400 -- 1450                                  45%                55%

over 1350 -- 1400                                  50%                50%

over 1300 -- 1350                                  55%                45%

over 1250 -- 1300                                  60%                40%

over 1200 -- 1250                                  65%                35%

over 1150 -- 1200                                  70%                30%

over 1100 -- 1150                                  75%                25%

over 1050 -- 1100                                  80%                20%

over 1000 -- 1050                                  85%                15%

1000 and under                                     90%                10%

When the S&P 500® Index moves into a new band on the table, the Fund promptly will rebalance the stock/bond mix to reflect the new S&P 500® Index price level by redeeming shares of some Portfolio Funds and purchasing shares of other Portfolio Funds. The only exception will be a "31-day Rule"; in order to reduce taxable events, after the Fund has increased its percentage allocation to either stock funds or bond funds, it will not decrease that allocation for at least 31 days. Following a change in the Fund's stock/bond mix, if the S&P 500® Index remains within the same band for a while, normal market fluctuations will change the values of the Fund's holdings of stock Portfolio Funds and bond Portfolio Funds. The Investment Manager will invest cash flows from sales (or redemptions) of Fund shares to bring the stock/bond mix back toward the allocation percentages for that S&P 500® Index band. For example, if the S&P 500® Index is in the 1150-1200 band, and the value of the holdings of the stock Portfolio Funds has dropped to 68% of the value of the holdings of all Portfolio Funds, the Investment Manager would invest new cash in the stock Portfolio Funds (or cash for redemptions would come from the bond Portfolio Funds). If the 31-day Rule is in effect, the Investment Manager will invest new cash at the stock/bond percentage allocation as of the latest rebalancing.

As an illustrative example, suppose the following:

 		              Level of the 		           How the Fund will invest

Date		          S and P 500(R) Index                       the Stock/Bond Assets

--------        ---------------------------------------         --------------------------------

Nov. 1             We begin when the market is 1380                  50% stocks, 50% bonds

Dec. 1             The S and P 500(R) goes to 1401              rebalance 45% stocks, 55% bonds

Dec. 6           The S and P 500(R) drops back to 1390              no reversal for 31 days

Jan. 2              The S and P 500(R) is at 1352               rebalance 50% stocks, 50% bonds

Jan. 20            The S and P 500(R) drops to 1349             rebalance 55% stocks, 45% bonds



      The market has made a continuation move by going through a second action level,

          not a reversal move, so the 31-day Rule does not apply in this case.



Jan. 30            The S and P 500(R) goes up to 1355               no reversal for 31 days

Feb. 20              The S and P 500(R) is at 1360              rebalance 50% stocks, 50% bonds

The following table shows the seven stock Portfolio Funds and three bond Portfolio Funds that the Fund currently uses in its "fund of funds" structure and the current allocation percentage for each Portfolio Fund within the stock or bond category. As described more fully below, the Investment Manager may substitute or add additional Portfolio Funds at any time, including funds introduced after the date of this prospectus. The allocation percentage within each stock/bond category is achieved by rebalancing the investments within the category whenever the S&P 500® Index moves into a new band on the allocation table, subject to the 31-day Rule described above. The Fund does not liquidate its investment in one Portfolio Fund in order to invest in another Portfolio Fund except in connection with a rebalancing due to a move of the S&P 500® Index into a new band (or due to a change by the Investment Manager in the stock/bond allocation table to the Portfolio Funds or to the relative allocation among them). Until a subsequent rebalancing, the Fund's investments in, and redemptions from, the stock Portfolio Funds or the bond Portfolio Funds are allocated among the Portfolio Funds in a manner that will reduce any deviation of the relative values of the Fund's holdings of the Funds from the allocation percentages shown below.

Allocation of Stock/Bond Assets Within Asset Classes

Stock Funds                                   Type of Fund 	             Allocation

-------------------------------------  ------------------------------------  -----------

Columbia Acorn Fund                    Small/Mid-cap growth                          15%

Columbia Acorn Select                  Mid-cap growth                                10%

Columbia Acorn International           Small/Mid-cap international growth            20%

Columbia Dividend Income Fund          Large-cap value                               20%

Columbia Large Cap Enhanced Core Fund  Large-cap blend                               10%

Columbia Contrarian Core Fund          Large-cap blend                               15%

Columbia Select Large Cap Growth Fund  Large-cap growth                              10%

Total                                                                               100%



Bond Funds                                    Type of Fund 	             Allocation

-------------------------------------  ------------------------------------  -----------

Columbia Intermediate Bond Fund        Intermediate-term bonds                       50%

Columbia Income Opportunities Fund     High-yield bonds                              30%

Columbia U.S. Treasury Index Fund      U.S. Treasury notes/bonds                     20%

Total                                                                               100%

The Investment Manager has the authority to review the Portfolio Funds and the relative stock/bond allocation percentages among them and to make any changes considered appropriate.

Each of the Portfolio Funds is currently managed by the Investment Manager or its affiliates. The Fund does not pay any sales load on its purchases of shares of the Portfolio Funds. On an annual basis, or on an "emergency" basis if necessary, the Investment Manager reviews the structure, allocation percentages and Portfolio Funds and makes any changes considered appropriate. The Investment Manager typically addresses the following questions:

• Should the stock/bond allocation table be revised (perhaps because the stock market has made a long-term move outside of the bands set forth above)?
• Should there be a change in the Portfolio Funds or should there be a change in the percentage allocations among the stock/bond funds (perhaps because of a change of portfolio managers, change of investment style, change in relative valuation or a reorganization of a Portfolio Fund)?

Any such changes by the Investment Manager are expected to be infrequent.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Allocation Risk – The Fund uses an asset allocation strategy in pursuit of its investment objective. There is a risk that the Fund's allocation among asset classes or investments will cause the Fund's shares to lose value or cause the Fund to underperform other funds with similar investment objectives, or that the investments themselves will not produce the returns expected.

• Investing in Other Funds Risk – The performance of the underlying fund(s) in which the Fund invests could be adversely affected if other entities that invest in the same underlying fund(s) make relatively large investments or redemptions in the underlying fund(s). In addition, because the expenses and costs of the underlying fund(s) are shared by investors in the underlying fund, redemptions by other investors in the underlying fund could result in decreased economies of scale and increased operating expenses for the underlying fund. The Fund, and its shareholders, indirectly bear a portion of the expenses of the underlying fund(s). These transactions might also result in higher brokerage, tax or other costs for the Fund. This risk may be particularly important when one investor owns a substantial portion of any underlying fund. In addition, the Investment Manager has the authority to change the underlying fund(s) in which the Fund invests or to change the percentage of the Fund's investments allocated to each underlying fund. If an underlying fund pays fees to the Investment Manager or its affiliates, such as advisory fees, this could result in the Investment Manager having a potential conflict of interest in selecting the underlying fund(s) in which the Fund invests or in determining the percentage of the Fund's investments allocated to each underlying fund. In addition, the underlying funds are themselves subject to Investment Strategy Risk.

The Fund is subject indirectly to the following risks of the Portfolio Funds:

• Market Risk – Market risk refers to the possibility that the market values of securities that a Portfolio Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Portfolio Fund. Accordingly, an investment in a Portfolio Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Portfolio Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Interest Rate Risk – Debt securities are subject to interest rate risk. In general, if prevailing interest rates rise, the values of debt securities will tend to fall, and if interest rates fall, the values of debt securities will tend to rise. Changes in the value of a debt security usually will not affect the amount of income a Portfolio Fund receives from it but may affect the value of the Portfolio Fund's shares. Interest rate risk is generally greater for debt securities with longer maturities/durations.

• Credit Risk – Credit risk applies to most debt securities, but is generally less of a factor for obligations backed by the "full faith and credit" of the U.S. Government. A Portfolio Fund could lose money if the issuer of a debt security owned by the Fund is unable or perceived to be unable to pay interest or repay principal when it becomes due. Various factors could affect the issuer's actual or perceived willingness or ability to make timely interest or principal payments, including changes in the issuer's financial condition or in general economic conditions. Debt securities backed by an issuer's taxing authority may be subject to legal limits on the issuer's power to increase taxes or otherwise to raise revenue, or may be dependent on legislative appropriation or government aid. Certain debt securities are backed only by revenues derived from a particular project or source, rather than by an issuer's taxing authority, and thus may have a greater risk of default.

• Low and Below Investment Grade Securities Risk – Debt securities with the lowest investment grade rating (e.g., BBB by Standard & Poor's, a division of the McGraw-Hill Companies, Inc. (S&P), or Fitch, Inc. (Fitch) or Baa by Moody's Investors Service, Inc. (Moody's)), or that are below investment grade (which are commonly referred to as "junk bonds") (e.g., BB or below by S&P or Fitch or Ba by Moody's) and unrated securities of comparable quality are more speculative than securities with higher ratings and may experience greater price fluctuations. These securities tend to be more sensitive to credit risk than higher-rated securities, particularly during a downturn in the economy, which is more likely to weaken the ability of the issuers to make principal and interest payments on these securities. These securities typically pay a premium – a higher interest rate or yield – because of the increased risk of loss, including default. These securities also are generally less liquid than higher-rated securities. The securities ratings provided by Moody's, S&P and Fitch are based on analyses by these ratings agencies of the credit quality of the securities and may not take into account every risk related to whether interest or principal will be timely repaid.

• Value Securities Risk – Value securities are securities of companies that may have experienced, for example, adverse business, industry or other developments or may be subject to special risks that have caused the securities to be out of favor and, in turn, potentially undervalued. The market value of a portfolio security may not meet the Investment Manager's future value assessment of that security, or may decline. There is also a risk that it may take longer than expected for the value of these investments to rise to the believed value. In addition, value securities, at times, may not perform as well as growth securities or the stock market in general, and may be out of favor with investors for varying periods of time.

• Growth Securities Risk – Because growth securities typically trade at a higher multiple of earnings than other types of securities, the market values of growth securities may be more sensitive to changes in current or expected earnings than the market values of other types of securities. In addition, growth securities, at times, may not perform as well as value securities or the stock market in general, and may be out of favor with investors for varying periods of time.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Portfolio Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Portfolio Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Index Risk – U.S. Treasury Index Fund's value will generally decline when the performance of its targeted index declines. Because U.S. Treasury Index Fund is designed to track an index before fees and expenses, U.S. Treasury Index Fund cannot purchase other securities that may help offset declines in its index. In addition, because U.S. Treasury Index Fund may not hold all issues included in its index, may not always be fully invested, and bears advisory, administrative and other expenses and transaction costs in trading securities, U.S. Treasury Index Fund's performance may fail to match the performance of its targeted index, after taking expenses into account. It is not possible to invest directly in an index.

• U.S. Government Obligations Risk – While U.S. Treasury obligations are backed by the "full faith and credit" of the U.S. Government, such securities are nonetheless subject to credit risk (i.e., the risk that the U.S. Government may be, or may be perceived to be, unable or unwilling to honor its financial obligations, such as making payments). Securities issued or guaranteed by federal agencies or authorities and U.S. Government-sponsored instrumentalities or enterprises may or may not be backed by the full faith and credit of the U.S. Government. For example, securities issued by the Federal Home Loan Mortgage Corporation, the Federal National Mortgage Association and the Federal Home Loan Banks are neither insured nor guaranteed by the U.S. Government. These securities may be supported by the ability to borrow from the U.S. Treasury or only by the credit of the issuing agency, authority, instrumentality or enterprise and, as a result, are subject to greater credit risk than securities issued or guaranteed by the U.S. Treasury. Securities guaranteed by the Federal Deposit Insurance Corporation under its Temporary Liquidity Guarantee Program (TLGP) are subject to certain risks, including whether such securities will continue to trade in line with recent experience in relation to treasury and government agency securities in terms of yield spread and the volatility of such spread, as well as uncertainty as to how such securities will trade in the secondary market and whether that market will be liquid or illiquid. The TLGP is subject to change. See ABOUT THE FUNDS' INVESTMENTS - U.S. Government and Related Obligations in the Statement of Additional Information for more information.

• Derivatives Risk – Derivatives are financial contracts whose values are, for example, based on (or "derived" from) traditional securities (such as a stock or bond), assets (such as a commodity like gold or a foreign currency), reference rates (such as LIBOR) or market indices (such as the S&P 500® Index). Derivatives involve special risks and may result in losses or may limit a Portfolio Fund's potential gain from favorable market movements. Derivative strategies often involve leverage, which may exaggerate a loss, potentially causing a Portfolio Fund to lose more money than it would have lost had it invested in the underlying security or other asset. The values of derivatives may move in unexpected ways, especially in unusual market conditions, and may result in increased volatility, among other consequences. The use of derivatives may also increase the amount of taxes payable by shareholders holding shares in a taxable account. Other risks arise from a Portfolio Fund's potential inability to terminate or to sell derivative positions. A liquid secondary market may not always exist for the Portfolio Fund's derivative positions at times when the Portfolio Fund might wish to terminate or to sell such positions. Over-the-counter instruments (investments not traded on an exchange) may be illiquid, and transactions in derivatives traded in the over-the-counter market are subject to the risk that the other party will not meet its obligations. The use of derivatives also involves the risks of mispricing or improper valuation and that changes in the value of the derivative may not correlate perfectly with the underlying security, asset, reference rate or index. A Portfolio Fund also may not be able to find a suitable derivative transaction counterparty, and thus may be unable to engage in derivative transactions when it is deemed favorable to do so, or at all. U.S. federal legislation has recently been enacted that provides for new clearing, margin, reporting and registration requirements for participants in the derivatives market. While the ultimate impact is not yet clear, these changes could restrict and/or impose significant costs or other burdens upon the Fund's participation in derivatives transactions. For more information on the risks of derivative investments and strategies, see the Statement of Additional Information.

• Convertible Securities Risk – Certain Portfolio Funds invest in convertible securities, which are subject to the usual risks associated with debt securities, such as interest rate risk and credit risk. Convertible securities also react to changes in the value of the common stock into which they convert. Because the value of a convertible security can be influenced by both interest rates and the common stock's market movements, a convertible security generally is not as sensitive to interest rates as a similar debt security, and generally will not vary in value in response to other factors to the same extent as the underlying common stock. In the event of a liquidation of the issuing company, holders of convertible securities would typically be paid before the company's common stockholders but after holders of any senior debt obligations of the company. A Portfolio Fund may be forced to convert a convertible security before it otherwise would choose to do so, which may decrease the Portfolio Fund's return.

• Non-Diversified Mutual Fund Risk – If a Portfolio Fund is non-diversified, that Portfolio Fund generally may invest a greater percentage of its total assets in the securities of fewer issuers than may a "diversified" fund. This increases the risk that a change in the value of any one investment held by the non-diversified Portfolio Fund could affect the overall value of the Portfolio Fund more than it would affect that of a diversified fund holding a greater number of investments. Accordingly, a non-diversified Portfolio Fund's value will likely be more volatile than the value of more diversified funds. A Portfolio Fund that is non-diversified may not operate as a non-diversified fund at all times.

• Technology Sector Risk – Companies in the technology sector are subject to significant competitive pressures, such as aggressive pricing of their products or services, new market entrants, competition for market share, short product cycles due to an accelerated rate of technological developments and the potential for limited earnings and/or falling profit margins. These companies also face the risks that new services, equipment or technologies will not be accepted by consumers and businesses or will become rapidly obsolete. These factors can affect the profitability of technology companies and, as a result, the value of their securities. Also, patent protection is integral to the success of many companies in the technology sector, and profitability can be affected materially by, among other things, the cost of obtaining (or failing to obtain) patent approvals, the cost of litigating patent infringement and the loss of patent protection for products (which significantly increases pricing pressures and can materially reduce profitability with respect to such products). In addition, many technology companies have limited operating histories. Prices of these companies' securities historically have been more volatile than other securities, especially over the short term. Because certain Portfolio Funds invest a significant portion of their net assets in the equity securities of technology companies, a Portfolio Fund's price may be more volatile than a fund that is invested in a more diverse range of market sectors.

• Health Care Sector Risk - Companies in the health care sector are subject to extensive government regulation. Their profitability can be affected significantly and adversely by restrictions on government reimbursement for medical expenses, government approval of medical products and services, competitive pricing pressures, an increased emphasis on outpatient and other alternative services and other factors. Patent protection is integral to the success of companies in the health care sector, and profitability can be affected materially by, among other things, the cost of obtaining (or failing to obtain) patent approvals, the cost of litigating patent infringement and the loss of patent protection for medical products (which significantly increases pricing pressures and can materially reduce profitability with respect to such products). Companies in the health care sector also potentially are subject to extensive product liability and other similar litigation. Companies in the health care sector are affected by the rising cost of medical products and services, and the effects of such rising costs can be particularly pronounced for companies that are dependent on a relatively limited number of products or services. Medical products also frequently become obsolete due to industry innovation or other causes. Because certain Portfolio Funds invest a significant portion of their net assets in the equity securities of health care companies, a Portfolio Fund's price may be more volatile than a fund that is invested in a more diverse range of market sectors.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class Z shares has varied from year to year.

Year by Year Total Return (%) as of December 31 Each Year

^[1]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    19.33%

Worst:   4th quarter 2008:   -19.26%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns for each period with those of the S&P 500® Index, the Fund's primary benchmark for equity securities, the Barclays U.S. Aggregate Bond Index, the Fund's primary benchmark for debt securities, the Lipper Flexible Portfolio Funds Index and a 50/50 Blended Benchmark. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. The Barclays U.S. Aggregate Bond Index is a market value-weighted index that tracks the daily price, coupon, pay-downs, and total return performance of fixed-rate, publicly placed, dollar-denominated, and non-convertible investment grade debt issues with at least $250 million par amount outstanding and with at least one year to final maturity. The Lipper Flexible Portfolio Funds Index is an equal-weighted index of the 30 largest mutual funds within the Flexible Portfolio fund classification, as defined by Lipper, and shows how the Fund's performance compares with the returns of an index of funds with similar investment objectives. The 50/50 Blended Benchmark was established by the Investment Manager to show how the Fund's performance compares to an equally weighted custom composite of the Fund's primary equity and primary debt benchmarks, the S&P 500® Index and the Barclays U.S. Aggregate Bond Index, respectively. The percentage of the Fund's assets allocated to underlying stock and bond Portfolio Funds will vary, and accordingly the composition of the Fund's portfolio will not always reflect the composition of the 50/50 Blended Benchmark.

Average Annual Total Returns (Columbia Thermostat Fund) (Columbia Thermostat Fund Z)	Inception Date	1 Year	5 Years	Life of Fund
Class Z Shares	Sep. 25, 2002	4.85%	4.21%	7.51%
Class Z Shares returns after taxes on distributions	Sep. 25, 2002	3.80%	3.12%	6.26%
Class Z Shares returns after taxes on distributions and sale of Fund shares	Sep. 25, 2002	3.15%	3.06%	5.97%
S&P 500® Index (reflects no deductions for fees, expenses or taxes)	Sep. 25, 2002	2.11%	(0.25%)	6.85%
Barclays U.S. Aggregate Bond Index (reflects no deductions for fees, expenses or taxes)	Sep. 25, 2002	7.84%	6.50%	5.33%
Lipper Flexible Portfolio Funds Index (reflects no deductions for taxes)	Sep. 25, 2002	(1.16%)	2.02%	7.10%
50-50 S&P 500/Barclays Capital Aggregate Bond (an equally weighted custom composite of the Fund's primary benchmarks for equity and debt securities, established by the Investment Manager; reflects no deductions for fees, expenses or taxes)	Sep. 25, 2002	5.28%	3.54%	6.43%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[2] Total annual Fund operating expenses include the annualized average weighted fees and expenses of acquired funds (underlying Portfolio Funds). As a result, the amount shown is higher than the ratio of expenses to average net assets included in Financial Highlights, which reflects only those expenses paid directly by the Fund.

[3] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that ordinary operating expenses (excluding distribution and service fees, interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies) do not exceed the annual rate of 0.25% of the Fund's average daily net assets, through April 30, 2013. The figure shown here is the amount of expected waivers and/or reimbursements. This fee and expense arrangement may only be modified or amended with approval from all parties to such arrangement, including the Fund and the Investment Manager.

[1] Year-to-date return as of March 31, 2012: 8.29%

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(Columbia Acorn International Select B) | (Columbia Acorn International Select)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn International Select)		Class B Shares (Columbia Acorn International Select B)
Maximum sales charge (load) imposed on purchases, as a % of offering price
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	[1]	5.00%

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn International Select)		Class B Shares (Columbia Acorn International Select B)
Management fees		0.94%
Distribution and/or service (Rule 12b-1) fees		0.75%
Other expenses	[1]	0.63%
Total annual Fund operating expenses		2.32%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class B shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn International Select) (USD $)	1 Year	3 Years	5 Years	10 Years
Class B Shares (Columbia Acorn International Select B)	735	1,024	1,440	2,481

Expense Example, No Redemption (Columbia Acorn International Select) (USD $)	1 Year	3 Years	5 Years	10 Years
Class B Shares (Columbia Acorn International Select B)	235	724	1,240	2,481

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 44% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 65% of its net assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom). The Fund also may invest up to 35% of its total assets in companies in emerging markets (for example, China, India and Brazil). The Fund generally invests in at least three countries other than the United States but may invest up to 25% of its total assets in securities of U.S. issuers.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $25 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $25 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $25 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $25 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $25 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies. The Fund also may invest in larger-sized companies.

The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to invest in a limited number of foreign companies (generally between 40-60), offering the potential to provide above-average growth over time.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class B shares has varied from year to year.

Year by Year Total Return (%) as of December 31 Each Year

^[1]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    23.09%

Worst:   3rd quarter 2008:   -24.96%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns, for each period, with those of the Standard & Poor's (S&P) Developed Ex-U.S. Between $2 Billion and $10 Billion® Index, the Fund's primary benchmark, and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index is a subset of the broad market selected by the index sponsor that represents the mid-cap developed market excluding the United States. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund's performance compares to a widely recognized broad based index of foreign market performance.

Average Annual Total Returns (Columbia Acorn International Select) (Columbia Acorn International Select B)	1 Year	5 Years	10 Years
Class B Shares	(14.99%)	(0.95%)	8.14%
Class B Shares returns after taxes on distributions	(15.22%)	(1.21%)	8.04%
Class B Shares returns after taxes on distributions and sale of Fund shares	(9.13%)	(0.69%)	7.33%
S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index (reflects no deductions for fees, expenses or taxes)	(14.01%)	(3.06%)	8.41%
MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)	(12.14%)	(4.72%)	4.67%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

[1] This charge decreases over time. See About Class B Shares - Sales Charges and Commissions for details.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] Year-to-date return as of March 31, 2012: 11.13%

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(Columbia Acorn Select Z) | (Columbia Acorn Select)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn Select)	Class Z Shares (Columbia Acorn Select Z)
Maximum sales charge (load) imposed on purchases, as a % of offering price	none
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn Select)		Class Z Shares (Columbia Acorn Select Z)
Management fees		0.82%
Distribution and/or service (Rule 12b-1) fees		none
Other expenses	[1]	0.18%
Total annual Fund operating expenses		1.00%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class Z shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn Select) (USD $)	1 Year	3 Years	5 Years	10 Years
Class Z Shares (Columbia Acorn Select Z)	102	318	552	1,225

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 21% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of companies with market capitalizations under $20 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $20 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $20 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $20 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $20 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Colombia).

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Fund may also invest in companies that the Investment Manager believes have good operational fundamentals but that the Investment Manager believes are undervalued due to negative investor sentiment related to company-specific or market-related conditions. Investments in turnaround and development stage companies may also be made when the Investment Manager believes potential returns outweigh risks of losses.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Opportunistic Investing Risk - Undervalued securities involve the risk that they may never reach their expected full market value, either because the market fails to recognize the security's intrinsic worth or the expected value was misgauged. Undervalued securities also may decline in price even though the Investment Manager believes they are already undervalued. Turnaround companies may never improve their fundamentals, may take much longer than expected to improve, or may improve much less than expected. Development stage companies could fail to develop and deplete their assets, resulting in large percentage losses.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class Z shares has varied from year to year.

Year by Year Total Return (%) as of December 31 Each Year

^[1]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    28.11%

Worst:   4th quarter 2008:   -30.14%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns for each period with those of the Standard & Poor's (S&P) MidCap 400® Index, the Fund's primary benchmark, and the S&P 500® Index. The S&P MidCap 400® Index is a market value-weighted index that tracks the performance of 400 mid-cap U.S. companies. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in companies with market capitalizations under $20 billion at the time of investment, the comparison to the S&P 500® Index is presented to show performance against a widely recognized market index.

Average Annual Total Returns (Columbia Acorn Select) (Columbia Acorn Select Z)	1 Year	5 Years	10 Years
Class Z Shares	(16.37%)	(1.07%)	6.05%
Class Z Shares returns after taxes on distributions	(16.87%)	(1.33%)	5.77%
Class Z Shares returns after taxes on distributions and sale of Fund shares	(10.60%)	(0.95%)	5.27%
S&P MidCap 400® Index (reflects no deductions for fees, expenses or taxes)	(1.73%)	3.32%	7.04%
S&P 500® Index (reflects no deductions for fees, expenses or taxes)	2.11%	(0.25%)	2.92%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] Year-to-date return as of March 31, 2012: 17.70%

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(Columbia Acorn International Select A,C & I) | (Columbia Acorn International Select)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds. More information about these and other discounts is available from your financial advisor, in the Choosing a Share Class section beginning on page 18 of this prospectus and in Appendix D to the Statement of Additional Information under Sales Charge Waivers beginning on page D-1.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn International Select A,C & I) (Columbia Acorn International Select)	Class A Shares		Class C Shares		Class I Shares
Maximum sales charge (load) imposed on purchases, as a % of offering price	5.75%
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[1]	1.00%	[2]

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn International Select A,C & I) (Columbia Acorn International Select)		Class A Shares	Class C Shares	Class I Shares
Management fees		0.94%	0.94%	0.94%
Distribution and/or service (Rule 12b-1) fees		0.25%	1.00%	none
Other expenses	[1]	0.43%	0.50%	0.14%
Total annual Fund operating expenses		1.62%	2.44%	1.08%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class A, Class C or Class I shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn International Select) (Columbia Acorn International Select A,C & I) (USD $)	1 Year	3 Years	5 Years	10 Years
Class A Shares	730	1,057	1,406	2,386
Class C Shares	347	761	1,301	2,776
Class I Shares	110	343	595	1,317

Expense Example, No Redemption (Columbia Acorn International Select) (USD $)	1 Year	3 Years	5 Years	10 Years
Class C Shares (Columbia Acorn International Select A,C & I)	247	761	1,301	2,776

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 44% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 65% of its net assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom). The Fund also may invest up to 35% of its total assets in companies in emerging markets (for example, China, India and Brazil). The Fund generally invests in at least three countries other than the United States but may invest up to 25% of its total assets in securities of U.S. issuers.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $25 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $25 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $25 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $25 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $25 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies. The Fund also may invest in larger-sized companies.

The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to invest in a limited number of foreign companies (generally between 40-60), offering the potential to provide above-average growth over time.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The inception date for the Fund's Class I shares is September 27, 2010. The returns shown for Class I shares include the returns of the Fund's Class Z shares for periods prior to the inception date of Class I shares. Except for differences in expenses, Class I shares have annual returns substantially similar to those of Class Z shares, which are not offered in this prospectus, because all classes of the Fund's shares invest in the same portfolio of securities.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class A shares has varied from year to year. These returns do not reflect deductions of sales charges, if any, paid by investors and would be lower if they did.

Year by Year Total Return (%) as of December 31 Each Year

^[1]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    23.32%

Worst:   3rd quarter 2008:   -24.85%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns, for each period, with those of the Standard & Poor's (S&P) Developed Ex-U.S. Between $2 Billion and $10 Billion® Index, the Fund's primary benchmark, and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index is a subset of the broad market selected by the index sponsor that represents the mid-cap developed market excluding the United States. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund's performance compares to a widely recognized broad based index of foreign market performance.

Average Annual Total Returns (Columbia Acorn International Select) (Columbia Acorn International Select A,C & I)	1 Year	5 Years	10 Years
Class A Shares	(15.28%)	(1.13%)	8.20%
Class A Shares returns after taxes on distributions	(15.64%)	(1.47%)	8.04%
Class A Shares returns after taxes on distributions and sale of Fund shares	(9.14%)	(0.86%)	7.38%
Class C Shares	(11.69%)	(0.75%)	8.03%
Class I Shares	(9.68%)	0.43%	9.24%
S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index (reflects no deductions for fees, expenses or taxes)	(14.01%)	(3.06%)	8.41%
MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)	(12.14%)	(4.72%)	4.67%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown only for Class A shares and will vary for other share classes.

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

[1] Contingent deferred sales charges (CDSC) on certain investments of between $1 million and $50 million redeemed within 18 months of purchase, charged as follows: 1.00% CDSC if redeemed within 12 months of purchase, and 0.50% CDSC if redeemed more than 12, but less than 18, months of purchase, with certain limited exceptions.

[2] This charge applies to investors who buy Class C shares and redeem them within one year of purchase, with certain limited exceptions.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] Year-to-date return as of March 31, 2012: 11.29%

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(Columbia Acorn International Select Z) | (Columbia Acorn International Select)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn International Select)	Class Z Shares (Columbia Acorn International Select Z)
Maximum sales charge (load) imposed on purchases, as a % of offering price	none
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn International Select)		Class Z Shares (Columbia Acorn International Select Z)
Management fees		0.94%
Distribution and/or service (Rule 12b-1) fees		none
Other expenses	[1]	0.31%
Total annual Fund operating expenses		1.25%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class Z shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn International Select) (USD $)	1 Year	3 Years	5 Years	10 Years
Class Z Shares (Columbia Acorn International Select Z)	127	397	686	1,511

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 44% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 65% of its net assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom). The Fund also may invest up to 35% of its total assets in companies in emerging markets (for example, China, India and Brazil). The Fund generally invests in at least three countries other than the United States but may invest up to 25% of its total assets in securities of U.S. issuers.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $25 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $25 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $25 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $25 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $25 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies. The Fund also may invest in larger-sized companies.

The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to invest in a limited number of foreign companies (generally between 40-60), offering the potential to provide above-average growth over time.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class Z shares has varied from year to year.

Year by Year Total Return (%) as of December 31 Each Year

^[1]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    23.44%

Worst:   3rd quarter 2008:   -24.76%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns, for each period, with those of the Standard & Poor's (S&P) Developed Ex-U.S. Between $2 Billion and $10 Billion® Index, the Fund's primary benchmark, and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index is a subset of the broad market selected by the index sponsor that represents the mid-cap developed market excluding the United States. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund's performance compares to a widely recognized broad based index of foreign market performance.

Average Annual Total Returns (Columbia Acorn International Select) (Columbia Acorn International Select Z)	1 Year	5 Years	10 Years
Class Z Shares	(9.76%)	0.41%	9.22%
Class Z Shares returns after taxes on distributions	(10.24%)	0.01%	9.02%
Class Z Shares returns after taxes on distributions and sale of Fund shares	(5.37%)	0.45%	8.31%
S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index (reflects no deductions for fees, expenses or taxes)	(14.01%)	(3.06%)	8.41%
MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)	(12.14%)	(4.72%)	4.67%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] Year-to-date return as of March 31, 2012: 11.37%

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(Columbia Acorn European Fund Z) | (Columbia Acorn European Fund)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn European Fund)	Class Z Shares (Columbia Acorn European Fund Z)
Maximum sales charge (load) imposed on purchases, as a % of offering price	none
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn European Fund)		Class Z Shares (Columbia Acorn European Fund Z)
Management fees		1.19%
Distribution and/or service (Rule 12b-1) fees		none
Other expenses	[1]	17.83%
Total annual Fund operating expenses		19.02%
Fee waivers and/or reimbursements	[2]	(17.52%)
Total annual Fund operating expenses after fee waivers and/or reimbursements		1.50%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class Z shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire on April 30, 2013, they are only reflected in the 1 year example and the first year of the 3 year example.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn European Fund) (USD $)	1 Year	3 Years
Class Z Shares (Columbia Acorn European Fund Z)	153	3,557

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 17% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 80% of its net assets (plus any borrowing for investment purposes) in European companies. Under normal circumstances, the Fund invests at least 70% of its total assets in companies in Western European countries (for example, the United Kingdom, Germany, France and Italy), but also may invest up to 30% of its total assets in companies in emerging Central and Eastern European countries (for example, Poland, the Czech Republic, Turkey and Cyprus), including up to 10% of its total assets in companies in Russia and the Ukraine. For purposes of the Fund's policies, the Fund may invest in a company if (i) it is domiciled in, or the principal trading market for its securities is in, a European country, (ii) it derives 50% or more of its economic value from goods produced, sales made or services performed or has at least 50% of its assets in a European country or (iii) it is a holding company that predominantly holds shares in such companies. The Fund may invest in a variety of countries, industries and sectors and does not attempt to invest a specific percentage of its assets in any given country, industry or sector.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to initially invest in a limited number of companies (generally under 100), offering the potential to provide above-average growth over time.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Currency Risk – Securities denominated in non-U.S. dollar currencies are subject to the risk that, for example, if the value of a foreign currency were to decline against the U.S. dollar, such decline would reduce the U.S. dollar value of any securities held by the Fund denominated in that currency.

• Special Situations Risk – Securities of companies that are involved in an initial public offering or a major corporate event, such as a business consolidation or restructuring, which may present special risk because of the high degree of uncertainty that can be associated with such events. Securities issued in initial public offerings often are issued by companies that are in the early stages of development, have a history of little or no revenues and may operate at a loss following the offering. It is possible that there will be no active trading market for the securities after the offering, and that the market price of the securities may be subject to significant and unpredictable fluctuations. Investing in special situations may have a magnified effect on the performance of funds with small amounts of assets.

Performance Information

Because the Fund commenced investment operations on August 19, 2011, no year-by-year total return bar chart or average annual total return table is being presented. The year-by year-total return bar chart and the average annual total return table will be provided after the Fund has annual returns for at least one calendar year.

Recent performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[2] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that the ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) do not exceed the annual rate of 1.50% of the Fund's average daily net assets attributable to Class Z shares, through April 30, 2013. The Investment Manager may recoup any fees waived and/or expenses reimbursed with respect to any share class of the Fund for a one-year period following the date of such fee waiver and/or reimbursement if such recovery does not cause the Fund's ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) to exceed the annual rates set forth in this prospectus, or to exceed such annual rate as may be in place at the time of the recoupment, whichever is less. This expense arrangement may only be modified or amended with approval from all parties to such arrangements, including the Fund and the Investment Manager.

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(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds. More information about these and other discounts is available from your financial advisor, in the Choosing a Share Class section beginning on page 19 of this prospectus and in Appendix D to the Statement of Additional Information under Sales Charge Waivers beginning on page D-1.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn International A,C,I,R & R5) (Columbia Acorn International)	Class A Shares		Class C Shares		Class I Shares	Class R Shares	Class R5 Shares
Maximum sales charge (load) imposed on purchases, as a % of offering price	5.75%
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[1]	1.00%	[2]

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn International A,C,I,R & R5) (Columbia Acorn International)		Class A Shares		Class C Shares		Class I Shares	Class R Shares	Class R5 Shares
Management fees		0.76%		0.76%		0.76%	0.76%	0.76%
Distribution and/or service (Rule 12b-1) fees		0.25%		1.00%		none	0.50%	none
Other expenses	[1]	0.38%		0.40%		0.10%	0.16%	0.11%
Total annual Fund operating expenses		1.39%		2.16%		0.86%	1.42%	0.87%
Fee waivers and/or reimbursements		(0.04%)	[2]	(0.02%)	[2]	none	none	none
Total annual Fund operating expenses after fee waivers and/or reimbursements		1.35%		2.14%		0.86%	1.42%	0.87%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class A, Class C, Class I, Class R or Class R5 shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn International) (Columbia Acorn International A,C,I,R & R5) (USD $)	1 Year	3 Years	5 Years	10 Years
Class A Shares	705	986	1,288	2,144
Class C Shares	317	674	1,158	2,491
Class I Shares	88	274	477	1,061
Class R Shares	145	449	776	1,702
Class R5 Shares	89	278	482	1,073

Expense Example, No Redemption (Columbia Acorn International) (USD $)	1 Year	3 Years	5 Years	10 Years
Class C Shares (Columbia Acorn International A,C,I,R & R5)	217	674	1,158	2,491

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 32% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 75% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Brazil).

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The inception date for the Fund's Class I shares is September 27, 2010 and the inception date for the Fund's Class R and R5 shares is August 2, 2011. The returns shown for Class I, Class R and Class R5 shares each include the returns of the Fund's Class Z shares (adjusted to reflect the higher class-related operating expenses of such classes, where applicable) for periods prior to the inception date of each class. Except for differences in expenses, these classes of shares each have annual returns substantially similar to those of Class Z shares, which are not offered in this prospectus, because all classes of the Fund's shares invest in the same portfolio of securities.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class A shares has varied from year to year. These returns do not reflect deductions of sales charges, if any, paid by investors and would be lower if they did.

Year by Year Total Return (%) as of December 31 Each Year

^[1]

Best and Worst Quarterly Returns During this Period

Best:    2nd quarter 2009:    33.20%

Worst:   3rd quarter 2008:   -23.79%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns, for each period, with those of the Standard & Poor's (S&P) Global Ex-U.S. Between $500 Million and $5 Billion® Index, the Fund's primary benchmark, the S&P Global Ex-U.S. SmallCap® Index and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Global Ex-U.S. Between $500 Million and $5 Billion® Index is a subset of the broad market selected by the index sponsor that represents the mid- and small-cap developed and emerging markets, excluding the United States. The S&P Global Ex-U.S. SmallCap® Index is an unmanaged index consisting of the bottom 20% of institutionally investable capital of developed and emerging countries, excluding the United States. The performance of the S&P Global Ex-U.S. Small Cap® Index is provided to show how the Fund's performance compares to foreign market performance with a similar geographic distribution and wider market cap range than the Fund's primary benchmark. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund's performance compares to a widely recognized broad based index of foreign market performance.

Average Annual Total Returns (Columbia Acorn International) (Columbia Acorn International A,C,I,R & R5)	1 Year	5 Years	10 Years
Class A Shares	(19.29%)	(1.33%)	9.20%
Class A Shares returns after taxes on distributions	(19.82%)	(1.79%)	8.73%
Class A Shares returns after taxes on distributions and sale of Fund shares	(12.29%)	(1.09%)	8.23%
Class C Shares	(15.85%)	(0.93%)	9.03%
Class I Shares	(14.02%)	0.22%	10.28%
Class R Shares	(14.60%)	(0.42%)	9.58%
Class R5 Shares	(14.07%)	0.19%	10.26%
S&P Global Ex-U.S. Between $500 Million and $5 Billion® Index (reflects no deductions for fees, expenses or taxes)	(16.94%)	(0.58%)	11.10%
S&P Global Ex-U.S. SmallCap® Index (reflects no deductions for fees, expenses or taxes)	(17.40%)	(2.14%)	10.33%
MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)	(12.14%)	(4.72%)	4.67%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown only for Class A shares and will vary for other share classes.

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

[1] Contingent deferred sales charges (CDSC) on certain investments of between $1 million and $50 million redeemed within 18 months of purchase, charged as follows: 1.00% CDSC if redeemed within 12 months of purchase, and 0.50% CDSC if redeemed more than 12, but less than 18, months of purchase, with certain limited exceptions.

[2] This charge applies to investors who buy Class C shares and redeem them within one year of purchase, with certain limited exceptions.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[2] Columbia Management Investment Services Corp., the Fund's transfer agent, has contractually agreed, through August 14, 2013, to waive a portion of total annual Fund operating expenses attributable to transfer agency fees incurred by Class A shares and Class C shares. Pursuant to this agreement, total annual Fund operating expenses will be reduced by 0.04% for Class A shares and 0.02% for Class C shares.

[1] Year-to-date return as of March 31, 2012: 14.99%

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(Columbia Acorn USA Z) | (Columbia Acorn USA)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn USA)	Class Z Shares (Columbia Acorn USA Z)
Maximum sales charge (load) imposed on purchases, as a % of offering price	none
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn USA)		Class Z Shares (Columbia Acorn USA Z)
Management fees		0.86%
Distribution and/or service (Rule 12b-1) fees		none
Other expenses	[1]	0.19%
Total annual Fund operating expenses		1.05%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class Z shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn USA) (USD $)	1 Year	3 Years	5 Years	10 Years
Class Z Shares (Columbia Acorn USA Z)	107	334	579	1,283

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 20% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 80% of its net assets (plus any borrowings for investment purposes) in U.S. companies.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund.

The Fund's past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

The bar chart below shows you how the performance of the Fund's Class Z shares has varied from year to year.

Year by Year Total Return (%) as of December 31 Each Year

^[1]

Best and Worst Quarterly Returns During this Period

Best:    3rd quarter 2009:    23.55%

Worst:   4th quarter 2008:   -27.96%

Average Annual Total Return as of December 31, 2011

The table compares the Fund's returns for each period with those of the Russell 2000 Index. This index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index.

Average Annual Total Returns (Columbia Acorn USA) (Columbia Acorn USA Z)	1 Year	5 Years	10 Years
Class Z Shares	(4.95%)	0.82%	6.30%
Class Z Shares returns after taxes on distributions	(5.04%)	0.52%	6.02%
Class Z Shares returns after taxes on distributions and sale of Fund shares	(3.10%)	0.69%	5.54%
Russell 2000 Index (reflects no deductions for fees, expenses or taxes)	(4.18%)	0.15%	5.62%

The after-tax returns shown in the table above are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or individual retirement accounts (IRAs).

Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[1] Year-to-date return as of March 31, 2012: 16.38%

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Annual Total Returns	0 Months Ended
	May 01, 2012
(Columbia Acorn Fund A,C & I) | (Columbia Acorn Fund) | Class A Shares
Bar Chart Table:
Annual Return 2002	(13.82%)
Annual Return 2003	44.85%
Annual Return 2004	21.05%
Annual Return 2005	12.76%
Annual Return 2006	14.13%
Annual Return 2007	7.39%
Annual Return 2008	(38.72%)
Annual Return 2009	39.26%
Annual Return 2010	25.61%
Annual Return 2011	(4.91%)
(Columbia Acorn Fund B) | (Columbia Acorn Fund) | Class B Shares
Bar Chart Table:
Annual Return 2002	(14.37%)
Annual Return 2003	43.89%
Annual Return 2004	20.15%
Annual Return 2005	11.98%
Annual Return 2006	13.43%
Annual Return 2007	6.76%
Annual Return 2008	(39.11%)
Annual Return 2009	38.37%
Annual Return 2010	24.81%
Annual Return 2011	(5.34%)
(Columbia Acorn Fund Z) | (Columbia Acorn Fund) | Class Z Shares
Bar Chart Table:
Annual Return 2002	(13.31%)
Annual Return 2003	45.68%
Annual Return 2004	21.51%
Annual Return 2005	13.11%
Annual Return 2006	14.45%
Annual Return 2007	7.69%
Annual Return 2008	(38.55%)
Annual Return 2009	39.65%
Annual Return 2010	26.00%
Annual Return 2011	(4.61%)
(Columbia Acorn International A,C,I,R & R5) | (Columbia Acorn International) | Class A Shares
Bar Chart Table:
Annual Return 2002	(16.46%)
Annual Return 2003	46.94%
Annual Return 2004	28.91%
Annual Return 2005	21.42%
Annual Return 2006	34.16%
Annual Return 2007	16.90%
Annual Return 2008	(46.09%)
Annual Return 2009	50.40%
Annual Return 2010	22.23%
Annual Return 2011	(14.37%)
(Columbia Acorn International B) | (Columbia Acorn International) | Class B Shares
Bar Chart Table:
Annual Return 2002	(17.07%)
Annual Return 2003	46.06%
Annual Return 2004	27.91%
Annual Return 2005	20.57%
Annual Return 2006	33.26%
Annual Return 2007	16.25%
Annual Return 2008	(46.41%)
Annual Return 2009	49.36%
Annual Return 2010	21.49%
Annual Return 2011	(14.92%)
(Columbia Acorn International Z) | (Columbia Acorn International) | Class Z Shares
Bar Chart Table:
Annual Return 2002	(16.10%)
Annual Return 2003	47.80%
Annual Return 2004	29.47%
Annual Return 2005	21.81%
Annual Return 2006	34.53%
Annual Return 2007	17.28%
Annual Return 2008	(45.89%)
Annual Return 2009	50.97%
Annual Return 2010	22.70%
Annual Return 2011	(14.06%)
(Columbia Acorn USA A,C & I) | (Columbia Acorn USA) | Class A Shares
Bar Chart Table:
Annual Return 2002	(18.97%)
Annual Return 2003	46.26%
Annual Return 2004	20.12%
Annual Return 2005	12.68%
Annual Return 2006	7.95%
Annual Return 2007	3.18%
Annual Return 2008	(39.38%)
Annual Return 2009	41.07%
Annual Return 2010	22.78%
Annual Return 2011	(5.21%)
(Columbia Acorn USA B) | (Columbia Acorn USA) | Class B Shares
Bar Chart Table:
Annual Return 2002	(19.48%)
Annual Return 2003	45.32%
Annual Return 2004	19.26%
Annual Return 2005	11.84%
Annual Return 2006	7.29%
Annual Return 2007	2.53%
Annual Return 2008	(39.75%)
Annual Return 2009	40.12%
Annual Return 2010	21.96%
Annual Return 2011	(5.68%)
(Columbia Acorn USA Z) | (Columbia Acorn USA) | Class Z Shares
Bar Chart Table:
Annual Return 2002	(18.49%)
Annual Return 2003	47.13%
Annual Return 2004	20.62%
Annual Return 2005	12.98%
Annual Return 2006	8.28%
Annual Return 2007	3.46%
Annual Return 2008	(39.22%)
Annual Return 2009	41.49%
Annual Return 2010	23.16%
Annual Return 2011	(4.95%)
(Columbia Acorn Select A,C & I) | (Columbia Acorn Select) | Class A Shares
Bar Chart Table:
Annual Return 2002	(8.17%)
Annual Return 2003	29.95%
Annual Return 2004	18.16%
Annual Return 2005	10.78%
Annual Return 2006	19.32%
Annual Return 2007	8.92%
Annual Return 2008	(49.31%)
Annual Return 2009	65.65%
Annual Return 2010	22.49%
Annual Return 2011	(16.65%)
(Columbia Acorn Select B) | (Columbia Acorn Select) | Class B Shares
Bar Chart Table:
Annual Return 2002	(8.77%)
Annual Return 2003	29.14%
Annual Return 2004	17.24%
Annual Return 2005	10.01%
Annual Return 2006	18.54%
Annual Return 2007	8.22%
Annual Return 2008	(49.62%)
Annual Return 2009	64.44%
Annual Return 2010	21.72%
Annual Return 2011	(17.11%)
(Columbia Acorn Select Z) | (Columbia Acorn Select) | Class Z Shares
Bar Chart Table:
Annual Return 2002	(7.81%)
Annual Return 2003	30.61%
Annual Return 2004	18.58%
Annual Return 2005	11.08%
Annual Return 2006	19.68%
Annual Return 2007	9.20%
Annual Return 2008	(49.18%)
Annual Return 2009	66.17%
Annual Return 2010	22.88%
Annual Return 2011	(16.37%)
(Columbia Acorn International Select A,C & I) | (Columbia Acorn International Select) | Class A Shares
Bar Chart Table:
Annual Return 2002	(15.16%)
Annual Return 2003	41.11%
Annual Return 2004	23.76%
Annual Return 2005	15.60%
Annual Return 2006	35.97%
Annual Return 2007	21.50%
Annual Return 2008	(42.30%)
Annual Return 2009	31.01%
Annual Return 2010	21.41%
Annual Return 2011	(10.11%)
(Columbia Acorn International Select B) | (Columbia Acorn International Select) | Class B Shares
Bar Chart Table:
Annual Return 2002	(15.72%)
Annual Return 2003	40.08%
Annual Return 2004	22.95%
Annual Return 2005	14.97%
Annual Return 2006	35.00%
Annual Return 2007	20.69%
Annual Return 2008	(42.68%)
Annual Return 2009	30.19%
Annual Return 2010	20.63%
Annual Return 2011	(10.64%)
(Columbia Acorn International Select Z) | (Columbia Acorn International Select) | Class Z Shares
Bar Chart Table:
Annual Return 2002	(14.89%)
Annual Return 2003	41.79%
Annual Return 2004	24.14%
Annual Return 2005	15.98%
Annual Return 2006	36.27%
Annual Return 2007	21.86%
Annual Return 2008	(42.10%)
Annual Return 2009	31.52%
Annual Return 2010	21.89%
Annual Return 2011	(9.76%)
(Columbia Thermostat Fund A&C) | (Columbia Thermostat Fund) | Class A Shares
Bar Chart Table:
Annual Return 2003	19.39%
Annual Return 2004	8.92%
Annual Return 2005	5.25%
Annual Return 2006	10.56%
Annual Return 2007	8.19%
Annual Return 2008	(30.67%)
Annual Return 2009	31.98%
Annual Return 2010	17.28%
Annual Return 2011	4.62%
(Columbia Thermostat Fund B) | (Columbia Thermostat Fund) | Class B Shares
Bar Chart Table:
Annual Return 2003	18.59%
Annual Return 2004	8.27%
Annual Return 2005	4.56%
Annual Return 2006	9.91%
Annual Return 2007	7.71%
Annual Return 2008	(31.10%)
Annual Return 2009	31.37%
Annual Return 2010	16.64%
Annual Return 2011	4.19%
(Columbia Thermostat Fund Z) | (Columbia Thermostat Fund) | Class Z Shares
Bar Chart Table:
Annual Return 2003	19.79%
Annual Return 2004	9.17%
Annual Return 2005	5.50%
Annual Return 2006	10.86%
Annual Return 2007	8.49%
Annual Return 2008	(30.53%)
Annual Return 2009	32.29%
Annual Return 2010	17.58%
Annual Return 2011	4.85%

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(Columbia Acorn European Fund A,C & I) | (Columbia Acorn European Fund)

Investment Objective

The Fund seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of eligible Columbia funds within the Columbia family of mutual funds. More information about these and other discounts is available from your financial advisor, in the Choosing a Share Class section beginning on page 18 of this prospectus and in Appendix D to the Statement of Additional Information under Sales Charge Waivers beginning on page D-1.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (Columbia Acorn European Fund A,C & I) (Columbia Acorn European Fund)	Class A Shares		Class C Shares		Class I Shares
Maximum sales charge (load) imposed on purchases, as a % of offering price	5.75%
Maximum deferred sales charge (load) imposed on redemptions, as a % of the lower of the original purchase price or net asset value	1.00%	[1]	1.00%	[2]

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses (Columbia Acorn European Fund A,C & I) (Columbia Acorn European Fund)		Class A Shares	Class C Shares	Class I Shares
Management fees		1.19%	1.19%	1.19%
Distribution and/or service (Rule 12b-1) fees		0.25%	1.00%	none
Other expenses	[1]	18.29%	19.93%	17.78%
Total annual Fund operating expenses		19.73%	22.12%	18.97%
Fee waivers and/or reimbursements	[2]	(17.98%)	(19.62%)	(17.66%)
Total annual Fund operating expenses after fee waivers and/or reimbursements		1.75%	2.50%	1.31%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in Class A, Class C or Class I shares of the Fund for the periods indicated,

• your investment has a 5% return each year, and

• the Fund's total annual operating expenses remain the same as shown in the table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire on April 30, 2013, they are only reflected in the 1 year example and the first year of the 3 year example.

Based on the assumptions listed above, your costs would be:

Expense Example (Columbia Acorn European Fund) (Columbia Acorn European Fund A,C & I) (USD $)	1 Year	3 Years
Class A Shares	743	4,038
Class C Shares	353	4,045
Class I Shares	133	3,537

Expense Example, No Redemption (Columbia Acorn European Fund) (USD $)	1 Year	3 Years
Class C Shares (Columbia Acorn European Fund A,C & I)	253	4,045

Remember this is an example only. Your actual costs may be higher or lower.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 17% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 80% of its net assets (plus any borrowing for investment purposes) in European companies. Under normal circumstances, the Fund invests at least 70% of its total assets in companies in Western European countries (for example, the United Kingdom, Germany, France and Italy), but also may invest up to 30% of its total assets in companies in emerging Central and Eastern European countries (for example, Poland, the Czech Republic, Turkey and Cyprus), including up to 10% of its total assets in companies in Russia and the Ukraine. For purposes of the Fund's policies, the Fund may invest in a company if (i) it is domiciled in, or the principal trading market for its securities is in, a European country, (ii) it derives 50% or more of its economic value from goods produced, sales made or services performed or has at least 50% of its assets in a European country or (iii) it is a holding company that predominantly holds shares in such companies. The Fund may invest in a variety of countries, industries and sectors and does not attempt to invest a specific percentage of its assets in any given country, industry or sector.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Except as noted above, under normal circumstances, the Fund may invest in other companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of its net assets would be invested in companies with market capitalizations under $5 billion.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to initially invest in a limited number of companies (generally under 100), offering the potential to provide above-average growth over time.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services that give the company a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

• Investment Strategy Risk – The Investment Manager uses the principal investment strategies and other investment strategies to seek to achieve the Fund's investment objective. There is no assurance that the Fund will achieve its investment objective. Investment decisions made by the Investment Manager in using these strategies may not produce the returns expected by the Investment Manager, may cause the Fund's shares to lose value or may cause the Fund to underperform other funds with similar investment objectives.

• Market Risk – Market risk refers to the possibility that the market values of securities that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. Security values may fall because of factors affecting individual companies, industries or sectors, or the markets as a whole, reducing the value of an investment in the Fund. Accordingly, an investment in the Fund could lose money over short or even long periods, or fail to increase in value. The market values of the securities the Fund holds also can be affected by changes or perceived changes in U.S. or foreign economies and financial markets, and the liquidity of these securities, among other factors. In general, equity securities tend to have greater price volatility than debt securities.

• Smaller Company Securities Risk – Securities of small- or mid-capitalization companies ("smaller companies") can, in certain circumstances, have a higher potential for gains than securities of large-capitalization companies but may also have more risk. For example, smaller companies may be more vulnerable to market downturns and adverse business or economic events than larger, more established companies because they may have more limited financial resources and business operations. These companies are also more likely than large-capitalization companies ("larger companies") to have more limited product lines and operating histories and to depend on smaller management teams. Their securities may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. In cases where the Fund takes significant positions in smaller companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in investment losses. In addition, some smaller companies may not be widely followed by the investment community, which can lower the demand for their stocks.

• Sector Risk – At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a broadly related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly.

• Foreign Securities Risk – Foreign securities are subject to special risks as compared to securities of U.S. issuers. For example, foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the value of foreign securities denominated in foreign currencies, or in U.S. dollars, without a change in the intrinsic value of those securities. Foreign securities may be less liquid than domestic securities so that the Fund may, at times, be unable to sell foreign securities at desirable times or prices. Brokerage commissions, custodial fees and other fees are also generally higher for foreign securities. The Fund may have limited or no legal recourse in the event of default with respect to certain foreign securities, including those issued by foreign governments. Foreign governments may impose potentially confiscatory withholding or other taxes, which could reduce the amount of income and capital gains available to distribute to shareholders. There is generally less publicly available information about foreign companies. Investments in foreign companies may be adversely affected by the impact of political, social or diplomatic events, possible imposition of currency exchange controls or possible seizure, expropriation or nationalization of a company or its assets resulting in a partial or total loss of an investment in such foreign companies. Accounting, auditing and financial reporting standards may also be less comprehensive and stringent than those applicable to domestic companies.

  Operational and Settlement Risks of Foreign Securities. The Fund's foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies ("foreign sub-custodians"), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

  Share Blocking. Share blocking refers to a practice in certain foreign markets under which an issuer's securities are blocked from trading at the custodian or sub-custodian level for a specified number of days before and, in certain instances, after a shareholder meeting where a vote of shareholders takes place. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period, because during the time shares are blocked, trades in such securities will not settle. It may be difficult or impossible to lift blocking restrictions, with the particular requirements varying widely by country. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

• Emerging Market Securities Risk – Securities issued by foreign governments or companies in emerging market countries, like Russia and those in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid social, political and economic development. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade, which makes them more sensitive to world commodity prices and economic downturns in other countries.

  Operational and Settlement Risks of Securities in Emerging Markets. In addition to having less developed securities markets, banks in emerging markets that are eligible foreign sub-custodians may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. Because settlement systems may be less organized than in developed markets and because delivery versus payment settlement may not be possible or reliable, there may be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Ownership of Russian securities poses particular risks because ownership records are typically maintained in a decentralized fashion by registrars who may not be subject to effective governmental supervision leading to the possibility that the Fund may lose its ownership rights. In such a case, it may be difficult for the Fund to enforce any rights it may have against the registrar or issuer of the securities.

  Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. For example, some emerging market countries may have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be traded internationally, or countries may have varying exchange rates. Some emerging market countries have a higher risk of currency devaluations, and some of these countries may experience sustained periods of high inflation or rapid changes in inflation rates which can have negative effects on a country's economy and securities markets. Corporate action procedures in emerging market countries may be less reliable and have limited or no involvement by the depositories and central banks. Lack of standard practices and payment systems can lead to significant delays in payment.

  Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Accordingly, foreign investors may be adversely affected by new or amended laws and regulations. In addition, the systems of corporate governance to which issuers in certain emerging markets are subject may be less advanced than the systems to which issuers located in more developed countries are subject, and therefore, shareholders of such issuers may not receive many of the protections available to shareholders of issuers located in more developed countries. These risks may be heightened in Russia.

• Currency Risk – Securities denominated in non-U.S. dollar currencies are subject to the risk that, for example, if the value of a foreign currency were to decline against the U.S. dollar, such decline would reduce the U.S. dollar value of any securities held by the Fund denominated in that currency.

• Special Situations Risk – Securities of companies that are involved in an initial public offering or a major corporate event, such as a business consolidation or restructuring, which may present special risk because of the high degree of uncertainty that can be associated with such events. Securities issued in initial public offerings often are issued by companies that are in the early stages of development, have a history of little or no revenues and may operate at a loss following the offering. It is possible that there will be no active trading market for the securities after the offering, and that the market price of the securities may be subject to significant and unpredictable fluctuations. Investing in special situations may have a magnified effect on the performance of funds with small amounts of assets.

Performance Information

Because the Fund commenced investment operations on August 19, 2011, no year-by-year total return bar chart or average annual total return table is being presented. The year-by year-total return bar chart and the average annual total return table will be provided after the Fund has annual returns for at least one calendar year.

Recent performance information can be obtained by calling toll-free 800.345.6611 or visiting www.columbiamanagement.com.

[1] Contingent deferred sales charges (CDSC) on certain investments of between $1 million and $50 million redeemed within 18 months of purchase, charged as follows: 1.00% CDSC if redeemed within 12 months of purchase, and 0.50% CDSC if redeemed more than 12, but less than 18, months of purchase, with certain limited exceptions.

[2] This charge applies to investors who buy Class C shares and redeem them within one year of purchase, with certain limited exceptions.

[1] Other expenses have been restated to reflect contractual changes to certain fees paid by the Fund.

[2] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that the ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) do not exceed the annual rates of 1.75%, 2.50% and 1.31% of the Fund's average daily net assets attributable to Class A, Class C and Class I shares, respectively, through April 30, 2013. The Investment Manager may recoup any fees waived and/or expenses reimbursed with respect to any share class of the Fund for a one-year period following the date of such fee waiver and/or reimbursement if such recovery does not cause the Fund's ordinary operating expenses (excluding interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) to exceed the annual rates set forth in this prospectus, or to exceed such annual rate as may be in place at the time of the recoupment, whichever is less. This expense arrangement may only be modified or amended with approval from all parties to such arrangements, including the Fund and the Investment Manager.