The Gabelli Utilities Fund

SUMMARY PROSPECTUS April 28, 2017

Class AAA (GABUX), A (GAUAX), C (GAUCX), I (GAUIX)

Before you invest, you may want to review the Fund’s Prospectus and Statement of Additional Information (“SAI”), which contain more information about the Fund and its risks. You can find the Fund’s Prospectus and SAI and other information about the Fund online at www.gabelli.com. You can also get this information at no cost by calling 800-422-3554 or by sending an email request to info@gabelli.com. The Fund’s Prospectus and SAI, both dated April 28, 2017, are incorporated by reference into this Summary Prospectus.

Investment Objective

The Gabelli Utilities Fund (the “Fund”) seeks to provide a high level of total return through a combination of capital appreciation and current income.

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. You may qualify for sales charge discounts on Class A shares if you and your family invest, or agree to invest in the future, at least $50,000 in Class A shares of the Gabelli family of mutual funds. More information about these and other discounts is available from your financial professional and in the section entitled, “Classes of Shares” on page 13 of the prospectus and in Appendix A, “Sales Charge Reductions and Waivers Available through Certain Intermediaries,” attached to the Fund’s prospectus.

Expense Example

This 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 in the Fund 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 remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

You would pay the following expenses if you did not redeem your shares of the Fund:

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 the Fund’s shares are held in a taxable account. These costs, which are not reflected in the 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 4% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 80% of its net assets in securities of domestic or foreign companies that are involved to a substantial extent in providing products, services or equipment for the generation or distribution of electricity, gas, and water and the provision of infrastructure operations or telecommunications services, such as telephone, telegraph, satellite, cable, microwave, radiotelephone, mobile communication and cellular, paging, electronic mail, videotext, voice communications, data communications, and internet and that derive at least 50% of their revenue or earnings from, or devote at least 50% of their assets to, utilities (each, a “Utility Company” and collectively, “Utility Companies”) that the Fund’s investment adviser, Gabelli Funds, LLC (the “Adviser”), believes have the potential to provide either capital appreciation or current income. The Adviser emphasizes quality in selecting utility investments, and looks for companies that have proven dividend records and sound financial structures. Generally, Utility Companies generate relatively predictable streams of revenue and income, and in the view of the Adviser, are likely to pay dividends. For additional information about selection of investments suitable for the Fund, see page 8 of the prospectus.

In selecting investments, the Adviser will consider factors such as: (i) the market price of the issuer’s common stock, earnings expectations, earnings and price histories, balance sheet characteristics, perceived management skills, and the conditions affecting the industry in which the issuer practices; (ii) the level of interest rates, local and national government regulations, the price and availability of materials used in the particular utility, environmental protection or energy conservation regulations, the level of demand for services, and the risks associated with constructing and operating certain kinds of facilities such as nuclear power facilities; (iii) the potential for capital appreciation of the stock; (iv) the dividend income generated by the stock; (v) the prices of the stock relative to other comparable stocks; and (vi) the diversification of the portfolio of the Fund as to issuers. The Adviser will also consider changes in economic and political outlooks as well as individual corporate developments. The Adviser will sell any Fund investments that lose their perceived value relative to other investments in the judgment of the portfolio management team.

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The Fund’s assets will be invested primarily in a broad range of readily marketable dividend paying common stocks in the utilities industry. Although many of these common stocks will pay above average dividends, the Fund will buy stock of those companies whose securities have the potential for their prices to increase, providing either capital appreciation or current income for the Fund. The Fund may also invest in master limited partnerships (“MLPs”).

The Fund may invest up to 40% of its total assets in securities of non-U.S. issuers.

Principal Risks

You may want to invest in the Fund if:

The Fund’s share price will fluctuate with changes in the market value of the Fund’s portfolio securities. Stocks are subject to market, economic, and business risks that may cause their prices to fluctuate. Holders of common stocks only have rights to the value in the company after all debts have been paid, and they could lose their entire investment in a company that encounters financial difficulty. The Fund is also subject to the following risks: that its portfolio companies will reduce or eliminate the dividend rate on the securities held by the Fund, that no event occurs to surface the value expected by the Adviser, or that regulatory actions adversely affect the Fund’s portfolio securities. As a consequence of its policy of concentrating in the utility industry, the Fund’s investments may be subject to greater risk and market fluctuation than a fund that has securities representing a broader range of alternatives. Foreign securities are subject to currency, information, and political risks.

Your investment in the Fund is not guaranteed; you may lose money by investing in the Fund. When you sell Fund shares, they may be worth less than what you paid for them.

The principal risks presented by the Fund are:

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Performance

The bar chart and table that follow provide an indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year, and by showing how the Fund’s average annual returns for one year, five years, and ten years compared with those of a broad based securities market index. As with all mutual funds, the Fund’s past performance (before and after taxes) does not predict how the Fund will perform in the future. Updated information on the Fund’s results can be obtained by visiting www.gabelli.com.

THE GABELLI UTILITIES FUND

(Total Returns for Class AAA Shares for the Years Ended December 31)

During the calendar years shown in the bar chart, the highest return for a quarter was 13.28% (quarter ended June 30, 2009), and the lowest return for a quarter was (12.26)% (quarter ended March 31, 2009).

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The returns shown for Class I shares prior to their first issuance date are those of Class AAA shares of the Fund. No returns are shown for Class T shares since they are not currently offered for sale. All classes of the Fund would have substantially similar annual returns because the shares are invested in the same portfolio of securities and the annual returns would differ only to the extent that the classes do not have the same expenses.

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 the investor’s tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their Fund shares through tax deferred arrangements, such as 401(k) plans or individual retirement accounts, including Roth IRAs and SEP IRAs (collectively, “IRAs”). After-tax returns are shown only for Class AAA shares and after-tax returns for other classes will vary due to the differences in expenses.

Management

The Adviser. Gabelli Funds, LLC

The Portfolio Manager. Mr. Mario J. Gabelli, CFA, Chief Investment Officer — Value Portfolios of the Adviser, has served as portfolio manager of the Fund since its inception on August 31, 1999.

Purchase and Sale of Fund Shares

The minimum initial investment for Class AAA, Class A, Class C, and Class T (when offered) shares is $1,000 ($250 for IRAs or Coverdell Education Savings Plans). There is no minimum initial investment for Class AAA, Class A, Class C, and Class T shares in an automatic monthly investment plan. Class T shares are not currently offered for sale.

Class I shares are available to investors with a minimum investment of at least $500,000 and purchasing the shares directly through G.distributors, LLC, the Fund’s distributor (“G.distributors” or the “Distributor”), or investors purchasing Class I shares through brokers or financial intermediaries that have entered into selling agreements with the Distributor specifically with respect to Class I shares. The Distributor reserves the right to waive or change minimum investment amounts. There is no minimum for subsequent investments.

You can purchase or redeem shares of the Fund on any day the New York Stock Exchange (“NYSE”) is open for trading (a “Business Day”). You may purchase or redeem Fund shares by written request via mail (The Gabelli Funds, P.O. Box 8308, Boston, MA 02266-8308), personal or overnight delivery (The Gabelli Funds, c/o BFDS, 30 Dan Road, Canton, MA 02021-2809), Internet, bank wire, or Automated Clearing House (“ACH”) system. You may also purchase Fund shares by telephone at 800-GABELLI (800-422-3554), if you have an existing account with banking instructions on file.

Fund shares can also be purchased or sold through registered broker-dealers or financial intermediaries that have entered into appropriate selling agreements with the Distributor. The broker-dealer or other financial intermediary will transmit these transaction orders to the Fund on your behalf and send you confirmation of your transactions and periodic account statements showing your investments in the Fund.

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Tax Information

The Fund expects that distributions will generally be taxable as ordinary income or long term capital gains, unless you are investing through a tax deferred arrangement, such as a 401(k) plan or an IRA.

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 related companies may pay the intermediary for the sale of the Fund shares and related services. 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.

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470 multi 2017

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