Columbia Acorn Trust

Supplement dated May 1, 2020

to the Prospectus, Summary Prospectus, and Statement of Additional Information (SAI) dated May 1, 2020

for each of the following Funds:

Fund

Columbia Acorn Emerging Markets Fund

Columbia Acorn Select

In February 2020, the Board of Trustees of each Fund, having determined that a reorganization of that Fund was in the best interest of the Fund and its shareholders, voted to approve an Agreement and Plan of Reorganization to reorganize the Fund (each, a Target Fund) with and into the corresponding acquiring fund presented in the table below (each, an Acquiring Fund). Pursuant to applicable law (including the Investment Company Act of 1940) the reorganizations may be implemented without shareholder approval. The reorganizations are expected to occur in the third quarter of 2020 and are expected to be tax-free reorganizations for U.S. federal income tax purposes. Additional information about the reorganizations will be made available to shareholders in a Combined Information Statement/Prospectus that was filed with the Securities and Exchange Commission on April 20, 2020 and will be delivered to shareholders prior to the reorganization date.

Target Fund	Acquiring Fund
Columbia Acorn Emerging Markets Fund	Columbia Acorn International
Columbia Acorn Select	Columbia Acorn Fund

The foregoing is not an offer to sell, nor a solicitation of an offer to buy, shares of any Acquiring Fund, nor is it a solicitation of any proxy. Because each Target Fund will reorganize into the corresponding Acquiring Fund on its reorganization date, you should consider the appropriateness of making a new or subsequent investment in the Target Fund prior to its reorganization date. You should consider the investment objectives, risks, strategies, fees and expenses of an Acquiring Fund and/or Target Fund carefully before investing. To obtain an Acquiring Fund's current prospectus, shareholder reports and other regulatory filings, contact your financial intermediary or visit columbiathreadneedleus.com.

Shareholders should retain this Supplement for future reference.

SUP000_00_096_(05/20)

Summary Prospectus

May 1, 2020

Columbia Acorn Family of Funds

Managed by Columbia Wanger Asset Management, LLC

Columbia Acorn Emerging Markets Fund^SM

Class		Ticker Symbol
A		CAGAX
Advisor (Class Adv)		CAERX
C		CGMCX

Class		Ticker Symbol
Institutional (Class Inst)		CEFZX
Institutional 2 (Class Inst2)		CANRX
Institutional 3 (Class Inst3)		CPHRX

Beginning on January 1, 2021, as permitted by regulations adopted by the Securities and Exchange Commission, paper copies of the Fund's annual and semiannual shareholder reports will no longer be sent by mail, unless you specifically request paper copies of the reports. Instead, the reports will be made available on the Fund's website (columbiathreadneedleus.com/investor/), and each time a report is posted you will be notified by mail and provided with a website address to access the report.

If you have already elected to receive shareholder reports electronically, you will not be affected by this change and you need not take any action. You may elect to receive shareholder reports and other communications from the Fund electronically at any time by contacting your financial intermediary (such as a broker-dealer or bank) or, for Fund shares held directly with the Fund, by calling 800.345.6611 or by enrolling in “eDelivery” by logging into your account at columbiathreadneedleus.com/investor/.

You may elect to receive all future reports in paper free of charge. If you invest through a financial intermediary, you can contact your financial intermediary to request that you continue receiving paper copies of your shareholder reports. If you invest directly with the Fund, you can call 800.345.6611 to let the Fund know you wish to continue receiving paper copies of your shareholder reports. Your election to receive paper reports will apply to all Columbia Funds held in your account if you invest through a financial intermediary or all Columbia Funds held with the fund complex if you invest directly with the Fund.

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, reports to shareholders, Statement of Additional Information and other information about the Fund online at https://www.columbiathreadneedleus.com/resources/literature. If you hold your Fund shares through a financial intermediary (such as a broker-dealer or bank), you can get this information at no cost by contacting that financial intermediary. If you hold your Fund shares directly with the Fund, you can 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, 2020.

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 Emerging Markets Fund^SM (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 26 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	1.25%	1.25%	1.25%	1.25%	1.25%	1.25%
Distribution and/or service (12b-1) fees	0.25%	0.00%	1.00%	0.00%	0.00%	0.00%
Other expenses^(c)	0.63%	0.63%	0.63%	0.63%	0.57%	0.52%
Total annual Fund operating expenses	2.13%	1.88%	2.88%	1.88%	1.82%	1.77%
Fee waivers and/or expense reimbursements^(d)	(0.58%)	(0.58%)	(0.58%)	(0.58%)	(0.58%)	(0.58%)
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	1.55%	1.30%	2.30%	1.30%	1.24%	1.19%

(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 fees paid by the Fund.
(d)	Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund, through April 30, 2021, so that ordinary operating expenses (excluding transaction costs and certain other investment-related expenses, 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 1.55% for Class A shares, 1.30% for Class Adv shares, 2.30% for Class C shares, 1.30% for Class Inst shares, 1.24% for Class Inst2 shares and 1.19% 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.

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.

1	Columbia Acorn Emerging Markets Fund^SM

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)	$724	$1,151	$1,603	$2,852
Class Adv (whether or not shares are redeemed)	$132	$ 535	$ 962	$2,154
Class C (assuming redemption of all shares at the end of the period)	$333	$ 837	$1,467	$3,163
Class C (assuming no redemption of shares)	$233	$ 837	$1,467	$3,163
Class Inst (whether or not shares are redeemed)	$132	$ 535	$ 962	$2,154
Class Inst2 (whether or not shares are redeemed)	$126	$ 516	$ 931	$2,090
Class Inst3 (whether or not shares are redeemed)	$121	$ 501	$ 905	$2,036

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 31% 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 (i) invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $10 billion at the time of initial investment (“Focus Stocks”) and (ii) may also invest in companies with market capitalizations above $10 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 $10 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 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 MSCI Emerging Markets SMID Cap Index (Net). In addition, the Fund may invest in certain developing market countries that are not included in the MSCI Emerging Markets SMID Cap Index (Net), 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 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.

Columbia Acorn Emerging Markets Fund^SM

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, among others. 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. The Fund may incur losses due to declines in the value of one or more securities in which it invests. These declines may be due to factors affecting a particular issuer, or the result of, among other things, political, regulatory, market, economic or social developments affecting the market(s) generally. In addition, turbulence in the financial markets generally and reduced liquidity in the equity, credit and/or fixed income markets more specifically may negatively affect many issuers, which could adversely affect the Fund, including by causing difficulty in pricing hard-to-value assets in thinly traded and closed markets, significant redemptions and operational challenges. Global economies and financial markets are increasingly interconnected, and conditions and events in one country, region, financial market or industry sector may adversely impact issuers in a different country, region, financial market or industry sector. These risks may be magnified if certain events or developments adversely interrupt the global supply chain; in these and other circumstances, such risks might affect companies worldwide. As a result, local, regional or global events such as terrorism, war, natural disasters, disease/virus outbreaks and epidemics or other public health crises, recessions, depressions or other events – or the potential for such events – could have a significant negative impact on global economic and market conditions.

The public health crisis caused by the novel coronavirus disease known as COVID-19 has become a pandemic that has resulted in, and may continue to result in, significant global economic and market volatility arising from disruptions in market access, resource availability, facilities operations, imposition of tariffs, export controls and supply chains, among other factors. These and related societal disruptions have been caused or exacerbated by, and may continue to be caused or exacerbated by, quarantines and travel restrictions, workforce displacement and loss in human and other resources. There is significant uncertainty surrounding the magnitude, duration, reach, costs and other effects of the COVID-19 global pandemic, including actions that have been or could be taken by governmental authorities or other third parties. The impacts, as well as the uncertainty over impacts yet to unfold, of COVID-19 – and any other infectious illness outbreaks, epidemics, pandemics or other public health crises that may arise in the future – could negatively affect global economies and markets in ways that cannot necessarily be foreseen. In addition, the impact of infectious illness outbreaks, and epidemics, pandemics and other public health crises in emerging market countries may be greater due to generally less established healthcare systems, governments and financial markets. Public health crises caused by the COVID-19 pandemic may exacerbate other pre-existing political, social and economic risks in certain countries or globally. The disruptions caused by COVID-19 could prevent the Investment Manager from executing advantageous investment decisions for the Fund in a timely manner and could negatively impact the Fund’s ability to achieve its investment objective. Any such event(s) could have a significant adverse impact on the value and risk profile of the Fund.

Liquidity and Trading Volume Risk. Due to market conditions, including uncertainty regarding the price of a security, it may be difficult for the Fund to buy or sell portfolio securities at a desirable time or price, which could result in investment losses. This risk of portfolio illiquidity is heightened with respect to small- and mid-cap securities, generally, and foreign small- and mid-cap securities in particular. The Fund may have to lower the selling price, liquidate other investments, or forego another, more appealing investment opportunity as a result of illiquidity in the markets. The Fund may also be limited in its ability to execute favorable trades in portfolio securities in response to changes in share prices and fundamentals, and may be forced to dispose of securities under disadvantageous circumstances and at a loss. As the Fund grows in size or, conversely, if it faces significant redemption pressure, these considerations take on increasing significance and may adversely impact performance.

Foreign Securities Risk. Investments in or exposure to foreign securities involve certain risks not associated with investments in or exposure to securities of U.S. companies. Foreign securities subject the Fund to the risks associated with investing in the particular country of an issuer, including political, regulatory, economic, social, diplomatic and other conditions or events (including, for example, military confrontations, war, terrorism and disease/virus outbreaks and epidemics), occurring in the country or region, as well as risks associated with less developed custody and settlement practices. Foreign securities may be more volatile and less liquid than securities

3	Columbia Acorn Emerging Markets Fund^SM

of U.S. companies, and are subject to the risks associated with potential imposition of economic and other sanctions against a particular foreign country, its nationals or industries or businesses within the country. In addition, foreign governments may impose withholding or other taxes on the Fund’s income, capital gains or proceeds from the disposition of foreign securities, which could reduce the Fund’s return on such securities.

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 foreign sub-custodians. Some countries have limited governmental oversight and regulation, 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. As a result, there is a risk that the security will not be delivered to the Fund or that payment will not be received. 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. In certain non-U.S. markets, an issuer’s securities are blocked from trading for a specified number of days before and, in certain instances, after a shareholder meeting. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period. 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, such as China, Russia and certain countries 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 changes or developments in social, political, economic or other conditions. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity (i.e., lower trading volumes and less liquidity) 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 and have fewer trading partners, which makes them more sensitive to world commodity prices and economic downturns in other countries, and some have a higher risk of currency devaluations.

Operational and Settlement Risks of Securities in Emerging Markets. Foreign sub-custodians in emerging markets 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. There may also 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.

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. Emerging market currencies may not have an active trading market and are subject to a higher risk of currency devaluations.

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.

Frontier Market Risk. Frontier market countries generally have smaller economies and even less developed capital markets than traditional emerging market countries (which themselves have increased investment risk relative to more developed market countries) and, as a result, the Fund’s exposure to the risks associated with investing in emerging market countries are magnified when the Fund invests in frontier market countries. Increased risks include: the potential for extreme price volatility and illiquidity in frontier market countries; government ownership or control of parts of the private sector and of certain companies; trade barriers, exchange controls, managed adjustments in relative currency values and other protectionist and similar 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.

Foreign Currency Risk. The performance of the Fund may be materially affected positively or negatively by foreign currency strength or weakness relative to the U.S. dollar, particularly if the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar.

Geographic Focus Risk. The Fund may be particularly susceptible to economic, political, regulatory or other events or conditions affecting issuers and countries within the specific geographic regions in which the Fund invests. The Fund’s NAV may be more volatile than the NAV of a more geographically diversified fund.

Columbia Acorn Emerging Markets Fund^SM

Asia Pacific Region. Many of the countries in the Asia Pacific region are considered underdeveloped or developing, including from a political, economic and/or social perspective, and may have relatively unstable governments and economies based on limited business, industries and/or natural resources or commodities. Events in any one country within the region may impact other countries in the region or the region as a whole. As a result, events in the region will generally have a greater effect on the Fund than if the Fund were more geographically diversified. This could result in increased volatility in the value of the Fund’s investments and losses for the Fund. Also, securities of some companies in the region can be less liquid than U.S. or other foreign securities, potentially making it difficult for the Fund to sell such securities at a desirable time and price.

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.

Small- and Mid-Cap Company Securities Risk. Investments in small- and mid-cap companies often involve greater risks than investments in larger, more established 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.

Sector Risk. At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business within one or more economic sectors. 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.

Financial Services Sector. The Fund may be more susceptible to the particular risks that may affect companies in the financial services sector than if it were invested in a wider variety of companies in unrelated sectors. Companies in the financial services sector are subject to certain risks, including the risk of regulatory change, decreased liquidity in credit markets and unstable interest rates. Such companies may have concentrated portfolios, such as a high level of loans to one or more industries or sectors, which makes them vulnerable to economic conditions that affect such industries or sectors. Performance of such companies may be affected by competitive pressures and exposure to investments, agreements and counterparties, including credit products that, under certain circumstances, may lead to losses (e.g., subprime loans). Companies in the financial services sector are subject to extensive governmental regulation that may limit the amount and types of loans and other financial commitments they can make, and the interest rates and fees they may charge. In addition, profitability of such companies is largely dependent upon the availability and the cost of capital.

Information Technology Sector. The Fund may be more susceptible to the particular risks that may affect companies in the information technology sector than if it were invested in a wider variety of companies in unrelated sectors. Companies in the information technology sector are subject to certain risks, including the risk that new services, equipment or technologies will not be accepted by consumers and businesses or will become rapidly obsolete. Performance of such companies may be affected by factors including obtaining and protecting patents (or the failure to do so) and significant competitive pressures, including aggressive pricing of their products or services, new market entrants, competition for market share and short product cycles due to an accelerated rate of technological developments. Such competitive pressures may lead to limited earnings and/or falling profit margins. As a result, the value of their securities may fall or fail to rise. In addition, many information technology sector companies have limited operating histories and prices of these companies’ securities historically have been more volatile than other securities, especially over the short term.

Issuer Risk. An issuer in which the Fund invests may perform poorly, and the value of its securities may therefore decline, which may negatively affect the Fund’s performance. Underperformance of an issuer 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, military confrontations, war, terrorism, disease/virus outbreaks and epidemics or other events, conditions and factors.

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 MSCI Emerging Markets SMID Cap Index (Net). The MSCI Emerging Markets SMID Cap Index (Net) captures mid- and small-cap representation across 26 emerging market countries. It has 2,267 constituents (as of March 31, 2020) and covers approximately 29% of the free float adjusted market capitalization in each country.

5	Columbia Acorn Emerging Markets Fund^SM

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 columbiathreadneedleus.com.

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	_{1st Quarter 2012}	_18.00%
	_Worst	_{3rd Quarter 2015}	_-17.21%

*	Year to Date return as of March 31, 2020: -31.75%

Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2019)

	Share Class Inception Date	1 Year	5 Years	Life of Fund
Class Inst	08/19/2011
returns before taxes		20.85%	1.41%	4.13%
returns after taxes on distributions		21.21%	1.35%	4.05%
returns after taxes on distributions and sale of Fund shares		12.70%	1.20%	3.37%
Class A returns before taxes	08/19/2011	13.60%	-0.06%	3.11%
Class Adv returns before taxes	11/08/2012	20.92%	1.40%	4.16%
Class C returns before taxes	08/19/2011	18.76%	0.40%	3.10%
Class Inst2 returns before taxes	11/08/2012	20.99%	1.49%	4.21%
Class Inst3 returns before taxes	06/13/2013	21.10%	1.54%	4.24%
MSCI Emerging Markets SMID Cap Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)		12.37%	3.43%	2.14%

Fund Management

Investment Manager: Columbia Wanger Asset Management, LLC

Portfolio Manager	Title	Role with Fund	Service with the Fund Since
Satoshi Matsunaga, CFA	Portfolio Manager and Analyst	Co-Portfolio Manager since 2015	2011
Charles C. Young	Portfolio Manager and Analyst	Co-Portfolio Manager since 2017	2011

Columbia Acorn Emerging Markets Fund^SM

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
columbiathreadneedleus.com/investor/		Columbia Management Investment Services Corp. P.O. Box 219104 Kansas City, MO 64121-9104		Columbia Management Investment Services Corp. c/o DST Asset Manager Solutions, Inc. 430 W 7^th Street, Suite 219104 Kansas City, MO 64105-1407		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:

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.

Columbia Acorn Family of Funds

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

columbiathreadneedleus.com

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