Columbia Funds Series Trust

Summary Prospectus

July 1, 2019

Columbia Small Cap Index Fund

Class		Ticker Symbol
A		NMSAX
Institutional (Class Inst)		NMSCX
Institutional 2 (Class Inst2)		CXXRX
Institutional 3 (Class Inst3)		CSPYX

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, dated July 1, 2019, and current Statement of Additional Information.

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 Small Cap Index Fund (the Fund) seeks total return before fees and expenses that corresponds to the total return of the Standard & Poor’s (S&P) SmallCap 600^® Index.

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 waivers. More information is available about these sales charge waivers from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 21 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)
	Classes A, Inst, Inst2 and Inst3
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 current net asset value)	None

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
	Class A	Class Inst	Class Inst2	Class Inst3
Management fees	0.20%	0.20%	0.20%	0.20%
Distribution and/or service (12b-1) fees	0.25%	0.00%	0.00%	0.00%
Other expenses	0.00%	0.00%	0.00%	0.00%
Total annual Fund operating expenses	0.45%	0.20%	0.20%	0.20%

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:

	1 year	3 years	5 years	10 years
Class A (whether or not shares are redeemed)	$46	$144	$252	$567
Class Inst (whether or not shares are redeemed)	$20	$ 64	$113	$255
Class Inst2 (whether or not shares are redeemed)	$20	$ 64	$113	$255
Class Inst3 (whether or not shares are redeemed)	$20	$ 64	$113	$255

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 22% of the average value of its portfolio.

1	Columbia Small Cap Index Fund

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 80% of its net assets (including the amount of any borrowings for investment purposes) in common stocks that comprise the S&P SmallCap 600 Index (the Index).

The Fund may invest in derivatives, such as futures (including equity index futures), for cash equitization purposes.

Different common stocks have different weightings in the Index, depending on the amount of stock outstanding and the stock’s current price. In seeking to match the performance of the Index, Columbia Management Investment Advisers, LLC (the Investment Manager) attempts to allocate the Fund’s assets among common stocks in approximately the same weightings as the Index. This is referred to as a passive or indexing approach to investing.

As a result of the Fund’s indexing approach to investing, the Fund will typically emphasize within the portfolio those economic sectors emphasized by the Index, such as the financial services sector.

The Fund attempts to achieve at least a 95% correlation between the performance of the Index and the Fund’s investment results, before fees and expenses.

Principal Risks

An investment in the Fund involves risks, including Passive Investment Risk, Correlation/Tracking Error Risk, Issuer Risk, and Market Risk. Descriptions of these and other principal risks of investing in the Fund are provided 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.

Correlation/Tracking Error Risk. The Fund’s value will generally decline when the performance of the Index declines. A number of factors may affect the Fund’s ability to achieve a high degree of correlation with the Index, and there is no guarantee that the Fund will achieve a high degree of correlation. Failure to achieve a high degree of correlation may prevent the Fund from achieving its investment objective. The Fund also bears management and other expenses and transaction costs in trading securities or other instruments, which the Index does not bear. Accordingly, the Fund’s performance will likely fail to match the performance of the Index, after taking expenses into account. It is not possible to invest directly in an index.

Derivatives Risk. Derivatives may involve significant risks. Derivatives are financial instruments with a value in relation to, or derived from, the value of an underlying asset(s) or other reference, such as an index, rate or other economic indicator (each an underlying reference). Derivatives may include those that are privately placed or otherwise exempt from SEC registration, including certain Rule 144A eligible securities. Derivatives could result in Fund losses if the underlying reference does not perform as anticipated. Use of derivatives is a highly specialized activity that can involve investment techniques, risks, and tax planning different from those associated with more traditional investment instruments. The Fund’s derivatives strategy may not be successful and use of certain derivatives could result in substantial, potentially unlimited, losses to the Fund regardless of the Fund’s actual investment. A relatively small movement in the price, rate or other economic indicator associated with the underlying reference may result in substantial loss for the Fund. Derivatives may be more volatile than other types of investments. The value of derivatives may be influenced by a variety of factors, including national and international political and economic developments. Potential changes to the regulation of the derivatives markets may make derivatives more costly, may limit the market for derivatives, or may otherwise adversely affect the value or performance of derivatives. Derivatives can increase the Fund’s risk exposure to underlying references and their attendant risks, such as credit risk, market risk, foreign currency risk and interest rate risk, while exposing the Fund to correlation risk, counterparty risk, hedging risk, inflation risk, leverage risk, liquidity risk, pricing risk and volatility risk.

Derivatives Risk – Futures Contracts Risk. A futures contract is an exchange-traded derivative transaction between two parties in which a buyer (holding the “long” position) agrees to pay a fixed price (or rate) at a specified future date for delivery of an underlying reference from a seller (holding the “short” position). The seller hopes that the market price on the delivery date is less than the agreed upon price, while the buyer hopes for the contrary. Certain futures contract markets are highly volatile, and futures contracts may be illiquid. Futures exchanges may limit fluctuations in futures contract prices by imposing a maximum permissible daily price movement. The Fund may be disadvantaged if it is prohibited from executing a trade outside the daily permissible price movement. At or prior to maturity of a futures contract, the Fund may enter into an offsetting contract and may incur a loss to the extent there has been adverse movement in futures contract prices. The liquidity of the futures markets depends on participants entering into offsetting transactions rather than making or taking delivery. To the extent participants make or take delivery, liquidity in the futures market could be reduced. Because of the low margin deposits normally required in futures trading, it is possible that the Fund may employ a high degree of leverage in the portfolio. As a result, a

Columbia Small Cap Index Fund

relatively small price movement in a futures contract may result in substantial losses to the Fund, exceeding the amount of the margin paid. For certain types of futures contracts, losses are potentially unlimited. Futures markets are highly volatile and the use of futures may increase the volatility of the Fund’s NAV. Futures contracts executed (if any) on foreign exchanges may not provide the same protection as U.S. exchanges. Futures contracts can increase the Fund’s risk exposure to underlying references and their attendant risks, such as credit risk, market risk, foreign currency risk and interest rate risk, while also exposing the Fund to correlation risk, counterparty risk, hedging risk, inflation risk, leverage risk, liquidity risk, pricing risk and volatility risk.

Issuer Risk. An issuer in which the Fund invests or to which it has exposure 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 or other events, conditions or factors.

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

Market Risk. 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.

Passive Investment Risk. The Fund is not “actively” managed and may be affected by a general decline in market segments related to its underlying index. The Fund invests in securities or instruments included in, or believed by the Investment Manager to be representative of, its underlying index, regardless of their investment merits. The Fund does not seek temporary defensive positions when markets decline or appear overvalued.

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, including the financial services 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 broadly the Fund invests, 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 real estate developers, which makes them vulnerable to economic conditions that affect that industry. Performance of such companies may be affected by competitive pressures and exposure to investments or agreements 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 interest rates and fees that they may charge. In addition, profitability of such companies is largely dependent upon the availability and the cost of capital.

3	Columbia Small Cap Index Fund

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 A 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 a broad measure of market performance.

The performance of one or more share classes shown in the table below begins before the indicated inception date for such share class. The returns shown for each such share class include the returns of the Fund’s Class A shares for periods prior to its inception date. Share classes with expenses that are higher than Class A shares will have performance that is lower than Class A shares. Except for differences in annual returns resulting from differences in expenses and sales charges (where applicable), the 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 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.

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	_{2nd Quarter 2009}	_21.02%
	_Worst	_{4th Quarter 2018}	_-20.21%

*	Year to Date return as of March 31, 2019: 11.57%

Average Annual Total Returns (for periods ended December 31, 2018)

	Share Class Inception Date	1 Year	5 Years	10 Years
Class A	10/15/1996
returns before taxes		-8.95%	5.82%	13.10%
returns after taxes on distributions		-11.03%	3.69%	11.54%
returns after taxes on distributions and sale of Fund shares		-3.58%	4.41%	10.83%
Class Inst returns before taxes	10/15/1996	-8.71%	6.09%	13.38%
Class Inst2 returns before taxes	11/08/2012	-8.72%	6.09%	13.28%
Class Inst3 returns before taxes	03/01/2017	-8.71%	5.93%	13.16%
S&P SmallCap 600 Index (reflects no deductions for fees, expenses or taxes)		-8.48%	6.34%	13.61%

Columbia Small Cap Index Fund

Fund Management

Investment Manager: Columbia Management Investment Advisers, LLC

Portfolio Manager	Title	Role with Fund	Managed Fund Since
Christopher Lo, CFA	Senior Portfolio Manager	Lead Portfolio Manager	2014
Vadim Shteyn	Associate Portfolio Manager	Portfolio Manager	2011

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
Class A	All accounts other than IRAs	$2,000	$100
Class A	IRAs	$1,000	$100
Class 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.

5	Columbia Small Cap Index Fund

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 Columbia Management Investment Advisers, LLC (the Investment Manager), Columbia Management Investment Distributors, Inc. (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. Ask your financial advisor or visit your financial intermediary’s website for more information.

Columbia Small Cap Index Fund

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

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