EXPRO811

Summary Prospectus
January 26, 2018

OAKMARK INTERNATIONAL SMALL CAP FUND

Investor Class

Advisor Class

Institutional Class

Service Class

OAKEX

OAYEX

OANEX

OAREX

Before you invest, you may want to review the Fund's prospectus and statement of additional information, which contain more information about the Fund and its risks. You can find the Fund's prospectus and other information about the Fund online at www.Oakmark.com/prospectus. You can also get this information at no cost by calling 1-800-OAKMARK or by sending an email request to Literature@Oakmark.com. The Fund's prospectus and statement of additional information, dated January 26, 2018, and as each may be further supplemented or amended, are incorporated by reference into this Summary Prospectus.

INVESTMENT OBJECTIVE

Oakmark International Small Cap Fund seeks long-term capital appreciation.

FEES AND EXPENSES OF THE FUND

Below are the fees and expenses that you would pay if you buy and hold shares of the Fund.

Shareholder Fees (fees paid directly from your investment)

Investor
Class

Advisor
Class

Institutional
Class

Service
Class

Maximum sales charge
(load) imposed on
purchases

None

Maximum deferred
sales charge (load)

None

Redemption fee (as a
percentage of
amount redeemed
on shares held for
90 days or less)

Exchange fee

None

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

	Investor Class			Advisor Class			Institutional Class			Service Class
Management fees		1.09	%		1.09	%		1.09	%		1.09	%
Distribution (12b-1) fees		None			None			None			None
Other expenses		0.27	%		0.12	%		0.05	%		0.57	%
Total Annual Fund Operating Expenses		1.36	%		1.21	%		1.14	%		1.66	%

Example. The 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 assumes that you invest $10,000 for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses were those reflected in the table.

Although your actual returns and expenses may be higher or lower, based on these assumptions your expenses would be:

	Investor Class		Advisor Class		Institutional Class		Service Class
1 Year	$	138	$	123	$	116	$	169
3 Years		431		384		362		523
5 Years		745		665		628		902
10 Years		1,635		1,466		1,386		1,965

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 34% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGY

The Fund invests primarily in a diversified portfolio of common stocks of non-U.S. companies. In determining whether an issuer is a U.S. or non-U.S. company, the Fund considers various factors including, its country of domicile, the primary stock exchange on which it trades, the location from which the majority of its revenue comes, and its reporting currency. Under normal market conditions, the Fund invests at least 80% of its net assets (plus any borrowings for investment purposes) in the stocks of "small cap companies." A small cap company is one whose market capitalization is no greater than the largest market capitalization of any company included in the S&P EPAC (Europe Pacific Asia Composite) Small Cap Index ($15.6 billion as of December 31, 2017).

The Fund may invest in non-U.S. markets throughout the world, including emerging markets. The Fund considers emerging markets to be markets located in countries classified as emerging or frontier markets by MSCI, and are generally located in the AsiaPacific region, Eastern Europe, the Middle East, Central and South America, and Africa. Ordinarily, the Fund will invest in the securities of at least five countries outside the U.S. There are no geographic limits on the Fund's non-U.S. investments.

The Fund uses a value investment philosophy in selecting equity securities. This value investment philosophy is based upon the belief that, over time, a company's stock price converges with the Adviser's estimate of its intrinsic or true business value. By "true business value," the Adviser means its estimate of the price a knowledgeable buyer would pay to acquire the entire business. The Adviser believes that investing in securities priced significantly below what it believes is their true business value presents the best opportunity to achieve the Fund's investment objective. A company trading below its estimated intrinsic value is sometimes referred to as trading at a discount.

The Adviser uses this value investment philosophy to identify companies that it believes have discounted stock prices compared to the companies' true business values. In assessing

such companies, the Adviser looks for the following characteristics, although the companies selected may not have all of these attributes: (1) free cash flows and intelligent investment of excess cash; (2) earnings that are growing and are reasonably predictable; and (3) high level of company management ownership.

Key Tenets of the Oakmark Value Investment Philosophy:

1. Buy businesses that are trading at a significant discount to the Adviser's estimate of the company's intrinsic value. At the time the Adviser buys a company, the Adviser wants the company's stock to be inexpensive relative to what it believes the entire business is worth.

2. Invest with companies expected to grow shareholder value over time. Value investors can sometimes fall into the trap of buying a stock that is inexpensive for a reason—because the company just does not grow. The Adviser looks for good quality, growing businesses with positive free cash flow and intelligent investment of cash.

3. Invest with management teams that think and act as owners. The Adviser seeks out companies with management teams that understand the dynamics of per share value growth and are focused on achieving such growth. Stock ownership and incentives that align managements' interests with those of shareholders are key components of this analysis.

In making its investment decisions, the Adviser uses a "bottom-up" approach focused on individual companies, rather than focusing on specific economic factors or specific industries. To facilitate its selection of investments that meet the criteria described above, the Adviser uses independent, in-house research to analyze each company. As part of this selection process, the Adviser's analysts typically visit companies and conduct other research on the companies and their industries.

Once the Adviser identifies a stock that it believes is selling at a significant discount to the Adviser's estimated intrinsic value and that the company has one or more of the additional qualities mentioned above, the Adviser may consider buying that stock for the Fund. The Adviser usually sells a stock when the price approaches its estimated value. This means the Adviser sets specific "buy" and "sell" targets for each stock the Fund holds. The Adviser monitors each portfolio holding and adjusts these price targets as warranted to reflect changes in a company's fundamentals.

The Adviser believes that holding a relatively small number of stocks allows its "best ideas" to have a meaningful impact on the Fund's performance. Therefore, the Fund's portfolio typically holds thirty to seventy stocks rather than hundreds, and a higher percentage of the Fund's total assets may at times also be invested in a particular region, sector or industry.

PRINCIPAL INVESTMENT RISKS

As an investor in the Fund, you should have a long-term perspective and be able to tolerate potentially wide fluctuations in the value of your Fund shares. Your investment in the Fund is subject to risks, including the possibility that the value of the Fund's portfolio holdings may fluctuate in response to events specific to the companies in which the Fund invests, as well as economic, political or social events in the U.S. or abroad and the Adviser's evaluation of those events, and the success of the Adviser in implementing the Fund's investment strategy. As a

result, when you redeem your Fund shares, they may be worth more or less than you paid for them.

Although the Fund makes every effort to achieve its investment objective, it cannot guarantee it will attain that investment objective. The following principal investment risks, which are described in alphabetical order and not in order of importance or potential exposure, can significantly affect the Fund's performance:

Common Stock Risk. Common stocks are subject to greater fluctuations in market value than other asset classes as a result of such factors as a company's business performance, investor perceptions, stock market trends and general economic conditions. The rights of common stockholders are subordinate to all other claims on a company's assets including, debt holders and preferred stockholders; therefore, the Fund could lose money if a company in which it invests becomes financially distressed.

Emerging Markets Risk. The risks of investing in non-U.S. securities may be heightened for securities of issuers located in emerging market countries. Emerging market countries tend to have economic structures that are less diverse and mature, and political systems that are less stable, than those of developed countries. In addition to all of the risks of investing in non-U.S. securities, emerging markets are more susceptible to governmental interference, local taxes being imposed on foreign investments, restrictions on gaining access to sales proceeds, and less liquid and efficient trading markets.

Focused Portfolio Risk. The Fund's portfolio tends to be invested in a relatively small number of stocks—thirty to seventy rather than hundreds. As a result, the appreciation or depreciation of any one security held by the Fund will have a greater impact on the Fund's net asset value than it would if the Fund invested in a larger number of securities. Although that strategy has the potential to generate attractive returns over time, it also increases the Fund's volatility and may lead to greater losses.

Market Capitalization Risk. Investing primarily in issuers in one market capitalization category carries the risk that due to current market conditions, that category may be out of favor with investors.

Market Risk. The Fund is subject to market risk—the risk that securities markets and individual securities will increase or decrease in value. Market risk applies to every market and every security. Security prices may fluctuate widely over short or extended periods in response to adverse issuer, political, regulatory, market, economic or other developments that may cause broad changes in market value, public perceptions concerning these developments, and adverse investor sentiment. In addition, securities markets tend to move in cycles. If there is a general decline in the securities markets, it is possible your investment may lose value regardless of the individual results of the companies in which the Fund invests. The magnitude of up and down price or market fluctuations over time is sometimes referred to as "volatility," which, at times, can be significant. In addition, different asset classes and geographic markets may experience periods of significant correlation with each other. As a result of this correlation, the securities and markets in which the Fund invests may experience volatility due to market, economic, political or social events and conditions that may not readily appear to directly relate to such securities, the securities' issuer or the markets in which they trade. In addition, some companies may have substantial foreign operations or holdings and may involve additional risks relating to those markets, including but not limited to political, economic, regulatory, or other conditions in foreign countries, as well as currency exchange rates.

Non-U.S. Securities Risk. Investments in securities issued by entities based outside the United States may involve risks relating to political, social and economic developments abroad, as well as risks resulting from the differences between the regulations to which U.S. and non-U.S. issuers and markets are subject. These risks may result in the Fund experiencing rapid and extreme value changes due to currency controls; different accounting, auditing, financial reporting, and legal standards and practices; political and diplomatic changes and developments; expropriation; changes in tax policy; a lack of available public information regarding non-U.S. issuers; greater market volatility; a lack of sufficient market liquidity; differing securities market structures; higher transaction costs; and various administrative difficulties, such as delays in clearing and settling portfolio transactions or in receiving payment of dividends. These risks may be heightened in connection with investments in issuers located in developing and emerging countries, and in issuers in more developed countries that conduct substantial business in such developing and emerging countries. Fluctuations in the exchange rates between currencies may negatively affect an investment in non-U.S. securities. The Fund may hedge its exposure to foreign currencies. Although hedging may be used to protect the Fund from adverse currency movements, the use of such hedges may reduce or eliminate the potentially positive effect of currency revaluations on the Fund's total return, and there is no guarantee that the Fund's hedging strategy will be successful.

Region, Sector or Industry Risk. If the Fund has invested a higher percentage of its total assets in a particular region, sector or industry, changes affecting that region, sector or industry, or the perception of that region, sector or industry, may have a significant impact on the performance of the Fund's overall portfolio. Individual regions, sectors or industries may be more volatile, and may perform differently, than the broader market.

Small Cap Securities Risk. Investments in small cap companies may be riskier than investments in larger, more established companies. The securities of smaller companies may trade less frequently and in smaller volumes, and as a result, may be less liquid than securities of larger companies. Therefore, when purchasing and selling smaller cap securities, the Fund may experience higher transactional costs due to the length of time that might be needed to purchase or sell such securities. Additionally, if the Fund is forced to sell securities to meet redemption requests or other cash needs, it may be forced to dispose of those securities under disadvantageous circumstances and at a loss. Smaller companies also may be more vulnerable to economic, market and industry changes. As a result, share price changes may be more sudden or erratic than the prices of other equity securities, especially over the short term. Because smaller companies may have limited product lines, markets or financial resources or may depend on a few key employees, they may be more susceptible to particular economic events or competitive factors than large capitalization companies.

Value Style Risk. Investing in "value" stocks presents the risk that the stocks may never reach what the Adviser believes are their full market values, either because the market fails to recognize what the Adviser considers to be the companies' true business values or because the Adviser misjudged those values. In addition, value stocks may fall out of favor with investors and underperform other investments during given periods.

Your investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. You may lose

money by investing in the Fund. The likelihood of loss may be greater if you invest for a shorter period of time.

PERFORMANCE INFORMATION

The bar chart and performance table below can help you evaluate the potential risk and reward of investing in the Fund by showing changes in the performance of the Fund's Investor Class Shares from year to year. The Fund's past performance (before and after taxes), as provided by the bar chart and performance table that follow, is not an indication of how the Fund will perform in the future. The performance table illustrates the volatility of the Fund's historical returns over various lengths of time and shows how the Fund's average annual returns compare with those of a broad measure of market performance. The Fund's Advisor Class and Institutional Class each commenced operations on November 30, 2016. Updated performance information is available at Oakmark.com or by calling 1-800-OAKMARK.

Since 2008, the highest and lowest quarterly returns for the Fund's Investor Class Shares were:

• Highest quarterly return: 43.7%, during the quarter ended June 30, 2009

• Lowest quarterly return: -27.3%, during the quarter ended December 31, 2008

Average Annual Total Returns for Periods Ended
December 31, 2017

	1 Year			5 Years			10 Years
International Small Cap Fund – Investor Class
Return before taxes		26.08	%		9.73	%		5.69	%
Return after taxes on distributions		25.07	%		8.62	%		4.89	%
Return after taxes on distributions and sale of Fund shares		15.68	%		7.55	%		4.41	%
Advisor Class
Return before taxes		26.20	%		None			None
Institutional Class
Return before taxes		26.31	%		None			None
Service Class
Return before taxes		25.72	%		9.41	%		5.39	%
MSCI World ex U.S. Small Cap Index (Net)		31.04	%		11.37	%		5.16	%

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor's tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts or individual retirement accounts. In some cases, the after-tax returns may exceed the return before taxes due to an assumed tax benefit from any losses on a sale of Fund shares at the end of the measurement period. After-tax returns are shown only for Investor Class Shares. After-tax returns for Service Class Shares, Advisor Class Shares, and Institutional Class Shares will vary from returns shown for Investor Class Shares.

INVESTMENT ADVISER

Harris Associates L.P. is the investment adviser to the International Small Cap Fund.

PORTFOLIO MANAGERS

David G. Herro, CFA, Michael L. Manelli, CFA and Justin D. Hance, CFA manage the Fund's portfolio. Mr. Herro is Deputy Chairman, Chief Investment Officer of International Equity and a portfolio manager of the Adviser. He joined the Adviser in 1992 and has managed the Fund since its inception in 2005. Mr. Manelli is a Vice President, portfolio manager and analyst of the Adviser. He joined the Adviser in 2005 and has managed the Fund since 2011. Mr. Hance is a Vice President, Director of International Research and a portfolio manager of the Adviser. He joined the Adviser in 2010 and has managed the Fund since 2016.

PURCHASE AND SALE OF FUND SHARES

Shares of the Fund may be purchased and sold (redeemed) on any business day, normally any day when the New York Stock Exchange is open for regular trading. Such purchases and redemptions can be made through a broker-dealer or other financial intermediary, or directly with the Fund by writing to The Oakmark Funds at P.O. Box 219558 Kansas City, MO 64121-9558, or accessing our website (Oakmark.com). You may pay brokerage commissions on your purchases and sales of Institutional Class shares, which are not described in this prospectus.

Investor Class Shares

The minimum initial investment for Investor Class Shares is $1,000, and the minimum for each subsequent investment is $100.

Advisor Class Shares

Advisor Class Shares are offered for purchase directly from the Fund with a minimum initial investment of $100,000 and through certain intermediaries who have entered into an agreement with the Fund's distributor and/or the Adviser.

Institutional Class Shares

Institutional Class Shares are offered for purchase directly from the Fund with a minimum initial investment of $1,000,000 and through certain intermediaries who have entered into an agreement with the Fund's distributor and/or the Adviser.

Service Class Shares

Service Class Shares are offered only for purchase through certain retirement plans, such as 401(k) and profit sharing plans. To purchase or redeem Service Class Shares you must do so through a financial intermediary.

TAX INFORMATION

The Fund's distributions may be taxable to you as ordinary income and/or capital gains, unless you are invested through a tax-deferred arrangement, such as a 401(k) plan or an individual retirement account.

PAYMENTS TO BROKER-DEALERS AND OTHER FINANCIAL INTERMEDIARIES

If you purchase shares of the Fund through a broker-dealer or other financial intermediary (such as a bank), the Fund and its distributor and/or the Adviser may pay the intermediary for services provided to the Fund and its shareholders. The Adviser and/or distributor may also pay the intermediary for the sale of Fund shares. These payments may create a conflict of interest by influencing the broker-dealer or other intermediary and your salesperson to recommend the Fund over another investment. Ask your salesperson or visit your financial intermediary's website for more information. No such payments are made with respect to Institutional Class.