Columbia Acorn Trust

Summary Prospectus

May 1, 2018

Columbia Acorn Family of Funds

Managed by Columbia Wanger Asset Management, LLC

Columbia Acorn USA®

Class		Ticker Symbol
A		LAUAX
Advisor (Class Adv)^(a)		CUSAX
C		LAUCX
Institutional (Class Inst)^(a)		AUSAX
Institutional 2 (Class Inst2)^(a)		CYSRX
Institutional 3 (Class Inst3)^(a)		CUSYX

(a)	Prior to November 1, 2017, Class Adv shares were known as Class R4 shares, Class Inst shares were known as Class Z shares, Class Inst2 shares were known as Class R5 shares, and Class Inst3 shares were known as Class Y shares.

Before you invest, you may want to review the Fund’s Prospectus, which contains more information about the Fund and its risks. You can find the Fund’s Prospectus, Statement of Additional Information and other information about the Fund online at https://www.columbiathreadneedleus.com/resources/literature. You can also get this information at no cost by calling 800.345.6611 or by sending an email to serviceinquiries@columbiathreadneedle.com. This Summary Prospectus incorporates by reference the Fund’s Prospectus and Statement of Additional Information, both dated May 1, 2018.

As with all mutual funds, the Securities and Exchange Commission has not approved or disapproved these securities or passed upon the adequacy of this prospectus. Any representation to the contrary is a criminal offense.

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 financial intermediary for effecting such transactions. Such commission rates are set by the financial intermediary and 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 is available about these and other sales charge discounts and waivers from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 18 of the Fund’s prospectus, in Appendix A to the prospectus beginning on page A-1 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)
	Class A	Class C	Classes Adv, Inst, Inst2 and Inst3
Maximum sales charge (load) imposed on purchases (as a % of offering price)	5.75%	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% ^(a)	1.00% ^(b)	None

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
	Class A	Class Adv	Class C	Class Inst	Class Inst2	Class Inst3
Management fees	0.90%	0.90%	0.90%	0.90%	0.90%	0.90%
Distribution and/or service (12b-1) fees	0.25%	0.00%	1.00%	0.00%	0.00%	0.00%
Other expenses^(c)	0.28%	0.28%	0.28%	0.28%	0.20%	0.13%
Acquired fund fees and expenses	0.01%	0.01%	0.01%	0.01%	0.01%	0.01%
Total annual Fund operating expenses^(d)	1.44%	1.19%	2.19%	1.19%	1.11%	1.04%
Less: Fee waivers and/or expense reimbursements^(e)	(0.02%)	(0.02%)	(0.02%)	(0.02%)	(0.03%)	(0.01%)
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	1.42%	1.17%	2.17%	1.17%	1.08%	1.03%

(a)	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.
(b)	This charge applies to redemptions within 12 months after purchase, with certain limited exceptions.
(c)	Other expenses have been restated to reflect current transfer agency fees paid by the Fund.
(d)	“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.
(e)	Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund, through April 30, 2019, so that ordinary operating expenses (excluding transaction costs and certain other investment-related expenses, interest and fees on borrowings, if any) do not exceed the annual rates of 1.42% for Class A shares, 1.17% for Class Adv shares, 2.17% for Class C shares, 1.17% for Class Inst shares, 1.08% for Class Inst2 shares and 1.03% for Class Inst3 shares. This arrangement may only be amended or terminated with approval from the Fund’s Board of Trustees and the Investment Manager. The fee waivers and/or expense reimbursements shown in the table also reflect the contractual agreement of the Fund’s transfer agent, Columbia Management Investment Services Corp. (the Transfer Agent), to waive a portion of its fees through June 30, 2019, such that the Fund’s transfer agency fees do not exceed the annual rate of 0.14% of the average daily net assets of each share class other than Class Inst2 and Class Inst3. With respect to Class Inst2 and Class Inst3 shares, the Transfer Agent has contractually agreed to waive a portion of its fees such that the Fund's transfer agency fees do not exceed the annual rates of 0.05% of the average daily net assets of Class Inst2 shares and 0.00% of the average daily net assets of Class Inst3 shares.

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

1	Columbia Acorn USA®

■	the Fund’s total annual operating expenses remain the same as shown in the Annual Fund Operating Expenses table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire as indicated in the preceding table, they are only reflected in the 1 year example and the first year of the other examples. Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:

	1 year	3 years	5 years	10 years
Class A (whether or not shares are redeemed)	$711	$1,002	$1,315	$2,198
Class Adv (whether or not shares are redeemed)	$119	$ 376	$ 652	$1,441
Class C (assuming redemption of all shares at the end of the period)	$320	$ 683	$1,173	$2,522
Class C (assuming no redemption of shares)	$220	$ 683	$1,173	$2,522
Class Inst (whether or not shares are redeemed)	$119	$ 376	$ 652	$1,441
Class Inst2 (whether or not shares are redeemed)	$110	$ 350	$ 609	$1,349
Class Inst3 (whether or not shares are redeemed)	$105	$ 330	$ 573	$1,270

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 84% 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.

Columbia Acorn USA®

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 Inst 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 Russell 2000 Growth Index.

The performance of one or more share classes shown in the Average Annual Total Returns table below includes the Fund’s Class Inst 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 in effect during the period indicated in the table 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 Inst shares and will vary for other share classes.

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.

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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%

*	Year to Date return as of March 31, 2018: 3.81%

Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2017)

	Share Class Inception Date	1 Year	5 Years	10 Years
Class Inst	09/04/1996
returns before taxes		19.44%	12.85%	8.17%
returns after taxes on distributions		11.14%	6.62%	4.94%
returns after taxes on distributions and sale of Fund shares		16.22%	9.29%	6.16%
Class A returns before taxes	10/16/2000	12.30%	11.24%	7.24%
Class Adv returns before taxes	11/08/2012	19.42%	12.85%	8.16%
Class C returns before taxes	10/16/2000	17.65%	11.80%	7.10%
Class Inst2 returns before taxes	11/08/2012	19.56%	12.96%	8.22%
Class Inst3 returns before taxes	11/08/2012	19.60%	13.02%	8.24%
Russell 2000 Growth Index (reflects no deductions for fees, expenses or taxes)		22.17%	15.21%	9.19%

Fund Management

Investment Manager: Columbia Wanger Asset Management, LLC

Portfolio Manager	Title	Role with Fund	Service with the Fund Since
Matthew A. Litfin, CFA	Director of Research (U.S.) and Portfolio Manager	Lead Portfolio Manager since 2016	2015
Richard Watson, CFA	Portfolio Manager and Analyst	Co-Portfolio Manager since November 2017	2006

Purchase and Sale of Fund Shares

You may purchase or redeem shares of the Fund on any business day by contacting the Fund in the ways described below:

Online		Regular Mail		Express Mail		By Telephone
investor.columbiathreadneedle.com/us		Columbia Funds, c/o Columbia Management Investment Services Corp. P.O. Box 8081 Boston, MA 02266-8081		Columbia Funds, c/o Columbia Management Investment Services Corp. 30 Dan Road, Suite 8081 Canton, MA 02021-2809		800.422.3737

You may purchase shares and receive redemption proceeds by electronic funds transfer, by check or by wire. If you maintain your account with a broker-dealer or other financial intermediary, you must contact that financial intermediary to buy, sell or exchange shares of the Fund through your account with the intermediary.

The minimum initial investment amounts for the share classes offered by the Fund are shown below:

Columbia Acorn USA®

Minimum Initial Investment

Class	Category of eligible account	For accounts other than systematic investment plan accounts	For systematic investment plan accounts
Classes A & C	All accounts other than IRAs	$2,000	$100
Classes A & C	IRAs	$1,000	$100
Classes Adv & Inst	All eligible accounts	$0, $1,000 or $2,000 depending upon the category of eligible investor	$100
Class Inst2	All eligible accounts	None	N/A
Class Inst3	All eligible accounts	$0, $1,000, $2,000 or $1 million depending upon the category of eligible investor	$100 (for certain eligible investors)

More information about these minimums can be found in the Buying, Selling and Exchanging Shares - Buying Shares section of the prospectus. There is no minimum additional investment for any share class.

Tax Information

The Fund normally distributes net investment income and net realized capital gains, if any, to shareholders. These distributions are generally taxable to you as ordinary income, qualified dividend income or capital gains, unless you are investing through a tax-advantaged account, such as a 401(k) plan or an IRA. If you are investing through a tax-advantaged account, you may be taxed upon withdrawals from that account.

Payments to Broker-Dealers and Other Financial Intermediaries

If you purchase the Fund through a broker-dealer or other financial intermediary (such as a bank), the Fund and its related companies – including the Investment Manager, the Distributor and Columbia Management Investment Services Corp. (the Transfer Agent) – may pay the intermediary for the sale of Fund shares and related services. These payments may create a conflict of interest by influencing the broker-dealer or other intermediary and your financial advisor to recommend the Fund over another investment. These potential conflicts of interest may be heightened with respect to broker-dealers owned by Ameriprise Financial and/or its affiliates. Ask your financial advisor or visit your financial intermediary's website for more information.

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Columbia Acorn Family of Funds

Columbia Threadneedle Investments is the global brand name of the Columbia and Threadneedle group of companies.

columbiathreadneedle.com/us

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