
ING Mutual Funds ING International Core Fund (“Fund”) Supplement dated September 20, 2013 to the Fund’s Class I and Class W Prospectus dated February 28, 2013; and to the Fund’s Class I and Class W Summary Prospectus dated February 28, 2013 (each a “Prospectus” and collectively “Prospectuses”) On September 12, 2013, the Fund’s Board of Trustees (“Board”) approved the removal of Thornburg Investment Management, Inc. (“Thornburg”) as a sub-adviser to the Fund effective close of business on November 22, 2013. Thornburg currently manages a portion of the Fund’s assets and Wellington Management Company, LLP manages the other portion of the Fund’s assets. From the close of business on November 8, 2013 through the close of business on November 22, 2013, the Fund will be in a “transition period” during which time a transition manager with sell all or most of the assets managed by Thornburg and the transition manager may hold a large portion of the Fund’s assets in temporary investments. During this time, the Fund may not be pursuing its investment objective and strategies, and limitation on permissible investments and investment restrictions will not apply. The sales and purchases of securities during the transition period are expected to result in significant buy and sell transactions. Such transactions may be made at a disadvantageous time and may result in the realization of taxable gains or losses for the Fund resulting in taxable distributions to the Fund’s shareholders. In addition, these transactions will also result in transactional costs, which are ultimately borne by the Fund’s shareholders. Effective on or about November 25, 2013, Wellington Management Company, LLP will be the sole sub-adviser managing all of the Fund’s assets. Effective on or about November 25, 2013, the Fund’s Prospectuses are hereby revised as follows: 1. The subsection entitled “Fees and Expenses of the Fund — Portfolio Turnover” of the Fund’s Prospectuses is hereby deleted and replaced with the following: Portfolio Turnover % of average value of portfolio 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 transactions costs and may mean higher taxes if you are investing in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Expense Examples, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 71% of the average value of its portfolio. At the close of business on November 22, 2013, Thornburg Investment Management, Inc. (“Thornburg”) will be terminated as a sub-adviser to the Fund. On or about November 25, 2013, Wellington Management Company, LLP (“Wellington Management”) will be the sole sub-adviser managing the Fund’s assets. During the period from the close of business November 8, 2013 through the close of business on November 22, 2013, the Fund will be in a transition period during which time all or most of the assets managed by Thornburg will be sold. These transactions will result in significant buy and sell transactions and could result in the realization of taxable gains or losses for the Fund resulting in taxable distributions to the Fund’s shareholders. In addition, these transactions will result in transaction costs which will be borne by the Fund’s shareholders. 2. The section entitled “Principal Investment Strategies” of the Fund’s Prospectuses is hereby deleted and replaced with the following: PRINCIPAL INVESTMENT STRATEGIES Under normal market conditions, the Fund invests at least 65% of its total assets in equity securities of companies located in a number of different countries other than the United States. The Fund may invest in countries with emerging securities markets. The Fund’s emerging markets exposure will generally not be greater than 10% above the emerging markets exposure of the MSCI All Country World ex-U.S. Index. Emerging markets will be defined as countries that are included in the MSCI Emerging Markets IndexSM. The Fund may also invest in depositary receipts of foreign issuers. The Fund may invest up to 15% of its assets in real estate investment trusts. The Fund may use derivatives, including futures, options, swaps, and forward contracts, typically for hedging purposes to reduce risk, such as interest rate risk, currency risk, and price risk. The Fund may invest in other investment companies, including exchange-traded funds, to the extent permitted under the Investment Company Act of 1940, as amended, and the rules, regulations, and exemptive orders thereunder (“1940 Act”). The sub-adviser (“Sub-Adviser”) conducts fundamental research on individual companies to identify securities for purchase or sale. Fundamental analysis of a company involves the assessment of such factors as its business environment, management quality, balance sheet, income statement, anticipated earnings, revenues and dividends, and other related measures and indicators of value. Wellington Management seeks to invest in companies with underappreciated assets, improving and/or sustainable return on capital, and/or stocks that it believes are mispriced by the market due to short-term issues. This proprietary research takes into account each company’s long-term history as well as Wellington Management’s analysts’ forward-looking estimates, and allows for a comparison of the intrinsic value of stocks on a global basis focusing on return on invested capital in conjunction with other valuation metrics. Portfolio construction is driven primarily by bottom-up stock selection, with region, country, and sector weightings being secondary factors. The Sub-Adviser may sell securities for a variety of reasons, such as to secure gains, limit losses, or redeploy assets into opportunities believed to be more promising, among others. The Fund may lend portfolio securities on a short-term or long-term basis, up to 331/3 % of its total assets. 3. The section entitled “Principal Risks” of the Fund’s Prospectuses is hereby deleted in its entirety and replaced with the following: PRINCIPAL RISKS You could lose money on an investment in the Fund. Any of the following risks, among others, could affect Fund performance or cause the Fund to lose money or to underperform market averages of other funds. Company. The price of a given company’s stock could decline or underperform for many reasons including, among others, poor management, financial problems, or business challenges. If a company declares bankruptcy or becomes insolvent, its stock could become worthless. Currency. To the extent that the Fund invests directly in foreign (non-U.S.) currencies or in securities denominated in, or that trade in, foreign (non-U.S.) currencies, it is subject to the risk that those (non-U.S.) currencies will decline in value relative to the U.S. dollar or, in the case of hedging positions, that the U.S. dollar will decline in value relative to the currency being hedged. Derivative Instruments. Derivative instruments are subject to a number of risks, including the risk of changes in the market price of the underlying securities, credit risk with respect to the counterparty, risk of loss due to changes in interest rates and liquidity risk. The use of certain derivatives may also have a leveraging effect which may increase the volatility of the Fund and reduce its returns. Foreign Investments/Developing and Emerging Markets. Investing in foreign (non-U.S.) securities may result in the Fund experiencing more rapid and extreme changes in value than a fund that invests exclusively in securities of U.S. companies due to: smaller markets; differing reporting, accounting, and auditing standards; nationalization, expropriation, or confiscatory taxation; foreign currency fluctuations, currency blockage, or replacement; potential for default on sovereign debt; or political changes or diplomatic developments. Foreign investment risks may be greater in developing and emerging markets than in developed markets. Liquidity. If a security is illiquid, the Fund might be unable to sell the security at a time when the Fund’s manager might wish to sell, and the security could have the effect of decreasing the overall level of the Fund’s liquidity. Further, the lack of an established secondary market may make it more difficult to value illiquid securities, which could vary from the amount the Fund could realize upon disposition. The Fund may make investments that become less liquid in response to market developments or adverse investor perception. The Fund could lose money if it cannot sell a security at the time and price that would be most beneficial to the Fund. Market. Stock prices may be volatile and are affected by the real or perceived impacts of such factors as economic conditions and political events. The stock market tends to be cyclical, with periods when stock prices generally rise and periods when stock prices generally decline. Any given stock market segment may remain out of favor with investors for a short or long period of time, and stocks as an asset class may underperform bonds or other asset classes during some periods. From time to time, the stock market may not favor the value-oriented securities in which the Fund invests. Rather, the market could favor growth-oriented securities or may not favor equities at all. Market Capitalization Stocks fall into three broad market capitalization categories - large, mid, and small. Investing primarily in one category carries the risk that, due to current market conditions, that category may be out of favor with investors. If valuations of large-capitalization companies appear to be greatly out of proportion to the valuations of mid- or small-capitalization companies, investors may migrate to the stocks of mid- and small-sized companies causing the Fund that invests in these companies to increase in value more rapidly than a fund that invests in larger, fully-valued companies. Investing in mid- and small-capitalization companies may be subject to special risks associated with narrower product lines, more limited financial resources, smaller management groups, and a more limited trading market for their stocks as compared with larger companies. As a result, stocks of mid- and small-capitalization companies may decline significantly in market downturns. Other Investment Companies. The main risk of investing in other investment companies, including exchange-traded funds, is the risk that the value of the securities underlying an investment company might decrease. Because the Fund may invest in other investment companies, you will pay a proportionate share of the expenses of those other investment companies (including management fees, administration fees, and custodial fees) in addition to the expenses of the Fund. Real Estate Companies and Real Estate Investment Trusts (“REITs”). Investing in real estate companies and REITs may subject the Fund to risks similar to those associated with the direct ownership of real estate, including losses from casualty or condemnation, changes in local and general economic conditions, supply and demand, interest rates, zoning laws, regulatory limitations on rents, property taxes, and operating expenses in addition to terrorist attacks, war, or other acts that destroy real property. Securities Lending. Securities lending involves two primary risks: “investment risk” and “borrower default risk.” Investment risk is the risk that the Fund will lose money from the investment of the cash collateral received from the borrower. Borrower default risk is the risk that the Fund will lose money due to the failure of a borrower to return a borrowed security in a timely manner. An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation, the Federal Reserve Board or any other government agency.

ING Mutual Funds

ING International Core Fund

(“Fund”)

Supplement dated September 20, 2013

to the Fund’s Class I and Class W

Prospectus dated February 28, 2013; and

to the Fund’s Class I and Class W

Summary Prospectus dated February 28, 2013

(each a “Prospectus” and collectively “Prospectuses”)

On September 12, 2013, the Fund’s Board of Trustees (“Board”) approved the removal of Thornburg Investment Management, Inc. (“Thornburg”) as a sub-adviser to the Fund effective close of business on November 22, 2013. Thornburg currently manages a portion of the Fund’s assets and Wellington Management Company, LLP manages the other portion of the Fund’s assets. From the close of business on November 8, 2013 through the close of business on November 22, 2013, the Fund will be in a “transition period” during which time a transition manager with sell all or most of the assets managed by Thornburg and the transition manager may hold a large portion of the Fund’s assets in temporary investments. During this time, the Fund may not be pursuing its investment objective and strategies, and limitation on permissible investments and investment restrictions will not apply. The sales and purchases of securities during the transition period are expected to result in significant buy and sell transactions. Such transactions may be made at a disadvantageous time and may result in the realization of taxable gains or losses for the Fund resulting in taxable distributions to the Fund’s shareholders. In addition, these transactions will also result in transactional costs, which are ultimately borne by the Fund’s shareholders. Effective on or about November 25, 2013, Wellington Management Company, LLP will be the sole sub-adviser managing all of the Fund’s assets.

Effective on or about November 25, 2013, the Fund’s Prospectuses are hereby revised as follows:

1. The subsection entitled “Fees and Expenses of the Fund — Portfolio Turnover” of the Fund’s Prospectuses is hereby deleted and replaced with the following:

Portfolio Turnover % of average value of portfolio

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 transactions costs and may mean higher taxes if you are investing in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Expense Examples, affect the Fund’s performance.

During the most recent fiscal year, the Fund’s portfolio turnover rate was 71% of the average value of its portfolio.

At the close of business on November 22, 2013, Thornburg Investment Management, Inc. (“Thornburg”) will be terminated as a sub-adviser to the Fund. On or about November 25, 2013, Wellington Management Company, LLP (“Wellington Management”) will be the sole sub-adviser managing the Fund’s assets. During the period from the close of business November 8, 2013 through the close of business on November 22, 2013, the Fund will be in a transition period during which time all or most of the assets managed by Thornburg will be sold. These transactions will result in significant buy and sell transactions and could result in the realization of taxable gains or losses for the Fund resulting in taxable distributions to the Fund’s shareholders. In addition, these transactions will result in transaction costs which will be borne by the Fund’s shareholders.

2. The section entitled “Principal Investment Strategies” of the Fund’s Prospectuses is hereby deleted and replaced with the following:

PRINCIPAL INVESTMENT STRATEGIES

Under normal market conditions, the Fund invests at least 65% of its total assets in equity securities of companies located in a number of different countries other than the United States. The Fund may invest in countries with emerging securities markets. The Fund’s emerging markets exposure will generally not be greater than 10% above the emerging markets exposure of the MSCI All Country World ex-U.S. Index. Emerging markets will be defined as countries that are included in the MSCI Emerging Markets IndexSM. The Fund may also invest in depositary receipts of foreign issuers. The Fund may invest up to 15% of its assets in real estate investment trusts.

The Fund may use derivatives, including futures, options, swaps, and forward contracts, typically for hedging purposes to reduce risk, such as interest rate risk, currency risk, and price risk.

The Fund may invest in other investment companies, including exchange-traded funds, to the extent permitted under the Investment Company Act of 1940, as amended, and the rules, regulations, and exemptive orders thereunder (“1940 Act”).

The sub-adviser (“Sub-Adviser”) conducts fundamental research on individual companies to identify securities for purchase or sale. Fundamental analysis of a company involves the assessment of such factors as its business environment, management quality, balance sheet, income statement, anticipated earnings, revenues and dividends, and other related measures and indicators of value. Wellington Management seeks to invest in companies with underappreciated assets, improving and/or sustainable return on capital, and/or stocks that it believes are mispriced by the market due to short-term issues. This proprietary research takes into account each company’s long-term history as well as Wellington Management’s analysts’ forward-looking estimates, and allows for a comparison of the intrinsic value of stocks on a global basis focusing on return on invested capital in conjunction with other valuation metrics. Portfolio construction is driven primarily by bottom-up stock selection, with region, country, and sector weightings being secondary factors.

The Sub-Adviser may sell securities for a variety of reasons, such as to secure gains, limit losses, or redeploy assets into opportunities believed to be more promising, among others.

The Fund may lend portfolio securities on a short-term or long-term basis, up to 331/3 % of its total assets.

3. The section entitled “Principal Risks” of the Fund’s Prospectuses is hereby deleted in its entirety and replaced with the following:

PRINCIPAL RISKS

You could lose money on an investment in the Fund. Any of the following risks, among others, could affect Fund performance or cause the Fund to lose money or to underperform market averages of other funds.

Company. The price of a given company’s stock could decline or underperform for many reasons including, among others, poor management, financial problems, or business challenges. If a company declares bankruptcy or becomes insolvent, its stock could become worthless.

Currency. To the extent that the Fund invests directly in foreign (non-U.S.) currencies or in securities denominated in, or that trade in, foreign (non-U.S.) currencies, it is subject to the risk that those (non-U.S.) currencies will decline in value relative to the U.S. dollar or, in the case of hedging positions, that the U.S. dollar will decline in value relative to the currency being hedged.

Derivative Instruments. Derivative instruments are subject to a number of risks, including the risk of changes in the market price of the underlying securities, credit risk with respect to the counterparty, risk of loss due to changes in interest rates and liquidity risk. The use of certain derivatives may also have a leveraging effect which may increase the volatility of the Fund and reduce its returns.

Foreign Investments/Developing and Emerging Markets. Investing in foreign (non-U.S.) securities may result in the Fund experiencing more rapid and extreme changes in value than a fund that invests exclusively in securities of U.S. companies due to: smaller markets; differing reporting, accounting, and auditing standards; nationalization, expropriation, or confiscatory taxation; foreign currency fluctuations, currency blockage, or replacement; potential for default on sovereign debt; or political changes or diplomatic developments. Foreign investment risks may be greater in developing and emerging markets than in developed markets.

Liquidity. If a security is illiquid, the Fund might be unable to sell the security at a time when the Fund’s manager might wish to sell, and the security could have the effect of decreasing the overall level of the Fund’s liquidity. Further, the lack of an established secondary market may make it more difficult to value illiquid securities, which could vary from the amount the Fund could realize upon disposition. The Fund may make investments that become less liquid in response to market developments or adverse investor perception. The Fund could lose money if it cannot sell a security at the time and price that would be most beneficial to the Fund.

Market. Stock prices may be volatile and are affected by the real or perceived impacts of such factors as economic conditions and political events. The stock market tends to be cyclical, with periods when stock prices generally rise and periods when stock prices generally decline. Any given stock market segment may remain out of favor with investors for a short or long period of time, and stocks as an asset class may underperform bonds or other asset classes during some periods. From time to time, the stock market may not favor the value-oriented securities in which the Fund invests. Rather, the market could favor growth-oriented securities or may not favor equities at all.

Market Capitalization Stocks fall into three broad market capitalization categories - large, mid, and small. Investing primarily in one category carries the risk that, due to current market conditions, that category may be out of favor with investors. If valuations of large-capitalization companies appear to be greatly out of proportion to the valuations of mid- or small-capitalization companies, investors may migrate to the stocks of mid- and small-sized companies causing the Fund that invests in these companies to increase in value more rapidly than a fund that invests in larger, fully-valued companies. Investing in mid- and small-capitalization companies may be subject to special risks associated with narrower product lines, more limited financial resources, smaller management groups, and a more limited trading market for their stocks as compared with larger companies. As a result, stocks of mid- and small-capitalization companies may decline significantly in market downturns.

Other Investment Companies. The main risk of investing in other investment companies, including exchange-traded funds, is the risk that the value of the securities underlying an investment company might decrease. Because the Fund may invest in other investment companies, you will pay a proportionate share of the expenses of those other investment companies (including management fees, administration fees, and custodial fees) in addition to the expenses of the Fund.

Real Estate Companies and Real Estate Investment Trusts (“REITs”). Investing in real estate companies and REITs may subject the Fund to risks similar to those associated with the direct ownership of real estate, including losses from casualty or condemnation, changes in local and general economic conditions, supply and demand, interest rates, zoning laws, regulatory limitations on rents, property taxes, and operating expenses in addition to terrorist attacks, war, or other acts that destroy real property.

Securities Lending. Securities lending involves two primary risks: “investment risk” and “borrower default risk.” Investment risk is the risk that the Fund will lose money from the investment of the cash collateral received from the borrower. Borrower default risk is the risk that the Fund will lose money due to the failure of a borrower to return a borrowed security in a timely manner.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation, the Federal Reserve Board or any other government agency.