Columbia Acorn USA

SUMMARY OF THE FUND

Investment Objective

Columbia Acorn USA^® (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. An investor transacting in a class of Fund shares without any front-end sales charge, contingent deferred sales charge, or other asset-based fee for sales or distribution may be required to pay a commission to the broker/financial intermediary for effecting such transactions. Such commissions are not reflected in the tables or the example below. You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 18 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees - Columbia Acorn USA	Class A		Class C		Class R4	Class R5	Class Y	Class Z
Maximum sales charge (load) imposed on purchases (as a % of offering price)	5.75%		none		none	none	none	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	1.00%	[1]	1.00%	[2]	none	none	none	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 A	Class C	Class R4	Class R5	Class Y	Class Z
Management fees		0.89%	0.89%	0.89%	0.89%	0.89%	0.89%
Distribution and/or service (12b-1) fees		0.25%	1.00%	none	none	none	none
Other expenses	[1]	0.27%	0.27%	0.27%	0.18%	0.13%	0.27%
Acquired fund fees and expenses		0.01%	0.01%	0.01%	0.01%	0.01%	0.01%
Total annual Fund operating expenses	[2],[3]	1.42%	2.17%	1.17%	1.08%	1.03%	1.17%

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 the applicable class of Fund shares 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 Annual Fund Operating Expenses table above.

Although your actual costs may be higher or lower, 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 A	711	998	1,307	2,179
Class C	320	679	1,164	2,503
Class R4	119	372	644	1,420
Class R5	110	343	595	1,317
Class Y	105	328	569	1,259
Class Z	119	372	644	1,420

Expense Example, No Redemption - Columbia Acorn USA - USD ($)	1 year	3 years	5 years	10 years
Class A	711	998	1,307	2,179
Class C	220	679	1,164	2,503
Class R4	119	372	644	1,420
Class R5	110	343	595	1,317
Class Y	105	328	569	1,259
Class Z	119	372	644	1,420

Portfolio Turnover

The Fund may pay 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 98% of the average value of its portfolio.

Principal Investment Strategies

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

Under normal circumstances, the Fund (i) 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 initial investment (“Focus Stocks”) and (ii) may also invest in companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of the Fund’s net assets would be invested in Focus Stocks. The Fund may continue to hold, and make additional investments in, Focus Stocks whose market capitalizations have grown to exceed $5 billion, regardless of whether the Fund’s investments in Focus Stocks are a majority of the Fund’s net assets.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of small- and mid-sized companies, 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 in which the company has 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

An investment in the Fund involves risks, including those described below. There is no assurance that the Fund will achieve its investment objective and you may lose money. The value of the Fund’s holdings may decline, and the Fund’s net asset value (NAV) and share price may go down. An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Active Management Risk. The Investment Manager’s active management of the Fund could cause the Fund to underperform its benchmark index and/or other funds with similar investment objectives and/or strategies.

Market Risk. Market risk refers to the possibility that the market values of securities or other investments that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. An investment in the Fund could lose money over short or long periods.

Small- and Mid-Cap Company Securities Risk. Investments in small- and mid-capitalization companies (small- and mid-cap companies) often involve greater risks than investments in larger, more established companies (larger companies) because small- and mid-cap companies tend to have less predictable earnings and may lack the management experience, financial resources, product diversification and competitive strengths of larger companies. Securities of small- and mid-cap companies may be less liquid and more volatile than the securities of larger companies.

Growth Securities Risk. Growth securities typically trade at a higher multiple of earnings than other types of equity securities. Accordingly, the market values of growth securities may never reach their expected market value and may decline in price. 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.

Issuer Risk. An issuer in which the Fund invests may perform poorly, and the value of its securities may therefore decline, which would negatively affect the Fund’s performance. Poor performance may be caused by poor management decisions, competitive pressures, breakthroughs in technology, reliance on suppliers, labor problems or shortages, corporate restructurings, fraudulent disclosures, natural disasters or other events, conditions or factors.

Sector Risk. At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a related group of industries within a sector. Companies in the same sector may be similarly affected by economic, regulatory, political or market events or conditions, which may make the Fund more vulnerable to unfavorable developments in that sector than funds that invest more broadly. Generally, the more the Fund diversifies its investments, the more it spreads risk and potentially reduces the risks of loss and volatility.

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 bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with the Fund’s primary benchmark, the Russell 2000 Growth Index, and the Fund's former primary benchmark, the Russell 2000 Index. Effective May 1, 2017, the Fund compares its performance to that of the Russell 2000 Growth Index. Prior to this date, the Fund compared its performance to that of the Russell 2000 Index. The Investment Manager believes that the Fund's portfolio will generally be more closely aligned with the Russell 2000 Growth Index than with the former core benchmark from an investment style perspective. Information on the Russell 2000 Index will be included for a one-year transition period.

The performance of one or more share classes shown in the Average Annual Total Returns table below includes the Fund’s Class Z share returns (adjusted to reflect the higher class-related operating expenses of such classes, where applicable) for periods prior to the indicated inception date of such share classes. Except for differences in fees and expenses, all share classes of the Fund would have substantially similar annual returns because all share classes of the Fund invest in the same portfolio of securities.

The after-tax returns shown in the Average Annual Total Returns table below 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-advantaged accounts such as 401(k) plans or Individual Retirement Accounts (IRAs). The after-tax returns are shown only for Class Z 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.

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 columbiathreadneedle.com/us.

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

Best and Worst Quarterly Returns
During the Period Shown in the Bar Chart

Best                                                          3rd Quarter 2009                                                        23.55%

Worst                                                       4th Quarter 2008                                                        -27.96%

Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2016)

Average Annual Total Returns - Columbia Acorn USA	Share Class Inception Date	1 Year	5 Years	10 Years
Class Z	Sep. 04, 1996	13.00%	12.77%	6.62%
Class Z | returns after taxes on distributions	Sep. 04, 1996	4.02%	7.82%	4.10%
Class Z | returns after taxes on distributions and sale of Fund shares	Sep. 04, 1996	14.38%	9.99%	5.24%
Class A	Oct. 16, 2000	6.19%	11.15%	5.71%
Class C	Oct. 16, 2000	11.29%	11.71%	5.56%
Class R4	Nov. 08, 2012	12.93%	12.76%	6.62%
Class R5	Nov. 08, 2012	13.09%	12.85%	6.66%
Class Y	Nov. 08, 2012	13.18%	12.90%	6.69%
Russell 2000 Growth Index (reflects no deductions for fees, expenses or taxes)		11.32%	13.74%	7.76%
Russell 2000 Index (reflects no deductions for fees, expenses or taxes)		21.31%	14.46%	7.07%

[1] This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.

[2] This charge applies to redemptions within 12 months after purchase, with certain limited exceptions.

[1] Other expenses have been restated and are based on estimated amounts for the Fund's current fiscal year, taking into consideration changes in the method of allocating transfer agent expenses among Class A, Class C, Class R4 and Class Z shares of the Fund.

[2] “Total annual Fund operating expenses” are higher than “Total gross expenses” shown in the Financial Highlights section of this prospectus because “Total gross expenses” were reduced due to an extraordinary reimbursement of expenses overbilled by a third party.

[3] “Total annual Fund operating expenses” include acquired fund fees and expenses (expenses the Fund incurs indirectly through its investments in other investment companies) and may be higher than “Total Net Expenses” shown in the Financial Highlights section of this prospectus because “Total Net Expenses” do not include acquired fund fees and expenses.

[1] Year to Date return as of March 31, 2017: 5.29%