The RBB Fund, Inc.

Robeco Investment Funds

Robeco WPG Core Bond Fund

Institutional Class

Investor Class

Retirement Class

(INVESTMENT PORTFOLIO OF THE RBB FUND, INC.)

Supplement dated August 6, 2007

to the Prospectuses dated December 31, 2006 (as revised January 1, 2007)

This Supplement provides new and additional information beyond that contained in the Prospectuses and should be read in conjunction with the Prospectuses.

THE FIRST PARAGRAPH UNDER “ROBECO WPG CORE BOND FUND – PRIMARY INVESTMENT STRATEGIES” ON PAGE 32 OF EACH OF THE INSTITUTIONAL CLASS PROSPECTUS AND INVESTOR CLASS PROSPECTUS AND ON PAGE 4 OF THE RETIREMENT CLASS PROSPECTUS IS AMENDED AND RESTATED AS FOLLOWS:

Investments: The Fund invests substantially all, but at least 80%, of its net assets (including any borrowings for investment purposes) in U.S. dollar denominated or quoted bonds issued by domestic or foreign companies or governmental entities. The Fund may invest in all types of bonds, including notes, mortgage-backed and asset-backed securities (including without limitation mortgage-backed derivative securities), convertible debt securities, municipal securities, short-term debt securities and other financial instruments, including derivatives, with economic characteristics similar to bonds. The may also invest in fixed income securities of all types, including preferred stock. The Fund will notify shareholders in writing at least 60 days prior to any change in the 80% described above.

Subject to the 80% policy described above, the Fund may invest up to 20% of its net assets in obligations of domestic and foreign issuers which are denominated in currencies other than the U.S. dollar and in obligations of issuers located in emerging countries denominated in any currency. The Fund may engage in credit default swaps as well as other types of derivative instruments, including financial futures contracts, options on futures contracts, currency swaps, mortgage swaps, total return swaps and interest rate swaps, and interest rate floors, caps and collars, for both speculative and hedging purposes and forward foreign currency exchange contracts for hedging purposes only. The Fund’s exposure to credit default swaps will not exceed 50% of the Fund’s total assets.

THE PARAGRAPHS ENTITLED “DERIVATIVE CONTRACTS” AND “FOREIGN SECURITIES” ON

PAGE 38 OF THE INVESTOR CLASS PROSPECTUS AND ON PAGE 9 OF THE RETIREMENT CLASS PROSPECTUS ARE HEREBY DELETED IN THEIR ENTIRETY.

THE FIRST AND THIRD SENTENCES IN THE PARAGRAPH ENTITLED “DERIVATIVE CONTRACTS” ON PAGE 48 OF THE INSTITUTIONAL CLASS PROSPECTUS ARE AMENDED AND RESTATED AS FOLLOWS:

In addition to the WPG Core Bond Fund, the WPG Large Cap Growth Fund and WPG Small Cap Value Fund may, but need not, use derivative contracts for any of the following purposes:

• To seek to hedge against the possible adverse impact of changes in stock market prices, currency exchange rates or interest rates in the market value of its securities or securities to be bought;

• As a substitute for buying or selling currencies or securities; or

• To seek to enhance the Fund’s return in non-hedging situations.

In addition to the WPG Core Bond Fund, the WPG Small Cap Value Fund may use derivative contracts involving foreign currencies.

THE FIRST TWO SENTENCES IN THE PARAGRAPH ENTITLED “FOREIGN SECURITIES” ON PAGE 48 OF THE INSTITUTIONAL CLASS PROSPECTUS ARE AMENDED AND RESTATED AS FOLLOWS:

In addition to the WPG Core Bond Fund, the WPG Large Cap Growth Fund and the WPG Small Cap Value Fund may invest in U.S. dollar-denominated or traded securities of foreign issuers and the WPG Small Cap Value Fund may invest in securities traded or denominated in foreign currencies.

THE FOLLOWING SUPPLEMENTS THE INFORMATION UNDER “ROBECO WPG CORE BOND FUND – KEY RISKS” ON PAGES 32-33 OF EACH OF THE INSTITUTIONAL CLASS PROSPECTUS AND INVESTOR CLASS PROSPECTUS AND ON PAGES 4-5 OF THE RETIREMENT CLASS PROSPECTUS:

• Investment in foreign securities also involves currency risk associated with securities that trade or are denominated in currencies other than the U.S. dollar and which may be affected by fluctuations in currency exchange rates. An increase in the strength of the U.S. dollar relative to a foreign currency may cause the U.S. dollar value of an investment in that country to decline. Foreign currencies also are subject to risks caused by inflation, interest rates, budget deficits and low savings rates, political factors and government controls.

• Investment in emerging market securities involves greater risk than that associated with investment in foreign securities of developed foreign countries. These risks include volatile currency exchange rates, periods of high inflation, increased risk of default, greater social, economic and political uncertainty and instability, less governmental supervision and regulation of securities markets, weaker auditing and financial reporting standards, lack of liquidity in the markets, and the significantly smaller market capitalizations of emerging market issuers.

• Investments in derivative instruments including futures, options on futures, swaps, interest rate caps, floors and collars and foreign currency transactions involve additional risk of loss. The Fund may enter into a derivative instruments for hedging purposes, for example, in an effort to preserve a return or spread, protect against currency fluctuations, protect against adverse price movements, manage portfolio duration or manage the Fund’s credit exposures. Even so, loss can result from a lack of correlation between changes in the value of derivative instruments and the portfolio assets (if any) being hedged, the potential illiquidity of the markets for derivative instruments, the failure of the counterparty to perform its contractual obligations, or the risks arising from margin requirements and related leverage factors associated with such transactions. The use of these management techniques also involves the risk of loss if the Adviser is incorrect in its expectation of fluctuations in securities prices, interest rates, currency prices or credit events. In addition, the Fund may invest in derivative instruments to seek to increase total return. Such investing is considered a speculative practice and presents even greater risk of loss.

Please retain this Supplement for future reference.

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The RBB Fund, Inc.

Robeco Investment Funds

Robeco WPG Core Bond Fund

Institutional Class

Investor Class

Retirement Class

(INVESTMENT PORTFOLIO OF THE RBB FUND, INC.)

Supplement dated August 6, 2007

to the Statement of Additional Information dated

December 31, 2006 (as revised January 1, 2007)

This Supplement provides new and additional information beyond that contained in the Statement of Additional Information and should be read in conjunction with the Statement of Additional Information.

THE FOLLOWING SUPPLEMENTS THE INFORMATION UNDER “INVESTMENT INSTRUMENTS AND POLICIES” IN THE FUND’S STATEMENT OF ADDITIONAL INFORMATION:

Credit Default Swaps, Interest Rate Swaps, Mortgage Swaps, Currency Swaps, Total Return Swaps, Options on Swaps and Interest Rate Caps, Floors and Collars. The WPG Core Bond Fund may enter into credit default, interest rate and total return swaps. The Fund may also enter into interest rate caps, floors and collars. In addition, the Fund may enter into mortgage swaps and currency swaps.

The Fund may enter into swap transactions for hedging purposes or to seek to increase total return. As examples, the Fund may enter into swap transactions for the purpose of attempting to obtain or preserve a particular return or spread at a lower cost than obtaining a return or spread through purchases and/or sales of instruments in other markets, to protect against currency fluctuations, as a duration management technique, to protect against any increase in the price of securities the Fund anticipates purchasing at a later date, or to gain exposure to certain markets in an economical way.

Swap agreements are two party contracts entered into primarily by institutional investors. In a standard “swap” transaction, two parties agree to exchange the returns (or differentials in rates of return) earned or realized on particular predetermined investments or instruments, which may be adjusted for an interest factor. The gross returns to be exchanged or “swapped” between the parties are generally calculated with respect to a “notional amount,” i.e., the return on or increase in value of a particular dollar amount invested at a particular interest rate, in a particular foreign currency or security, or in a “basket” of securities representing a particular index. As examples, credit default swaps involve the receipt of floating or fixed rate payments in exchange for assuming potential credit losses of an underlying security. Credit default swaps give one party to a transaction the right to dispose of or acquire an asset (or group of assets), or the right to receive from or make a payment to the other party, upon the occurrence of specified credit events. Interest rate swaps involve the exchange by the Fund with another party of their respective commitments to pay or receive interest, such as an exchange of fixed-rate payments for floating rate payments. Mortgage swaps are similar to interest rate swaps in that they represent commitments to pay and receive interest. The notional principal amount, however, is tied to a reference pool or pools of mortgages. Currency swaps involve the exchange of the parties’ respective rights to make or receive payments in specified currencies. Total return swaps are contracts that obligate a party to pay or receive interest in exchange for payment by the other party of the total return generated by a security, a basket of securities, an index, or an index component.

The purchase of an interest rate cap entitles the purchaser, to the extent that a specified index exceeds a predetermined interest rate, to receive payment of interest on a notional principal amount from the party selling such interest rate cap. The purchase of an interest rate floor entitles the purchaser, to the extent that a specified

index falls below a predetermined interest rate, to receive payments of interest on a notional principal amount from the party selling the interest rate floor. An interest rate collar is the combination of a cap and a floor that preserves a certain return within a predetermined range of interest rates.

A great deal of flexibility is possible in the way swap transactions are structured. However, generally the Fund will enter into credit default, interest rate, total return and mortgage swaps on a net basis, which means that the two payment streams are netted out, with the Fund receiving or paying, as the case may be, only the net amount of the two payments. Credit default, interest rate, total return and mortgage swaps do not normally involve the delivery of securities, other underlying assets or principal. Accordingly, the risk of loss with respect to credit default, interest rate, total return and mortgage swaps is normally limited to the net amount of payments that a Fund is contractually obligated to make. If the other party to a credit default, interest rate, total return or mortgage swap defaults, the Fund’s risk of loss consists of the net amount of payments that the Fund is contractually entitled to receive, if any. In contrast, currency swaps may involve the delivery of the entire principal amount of one designated currency in exchange for the other designated currency. Therefore, the entire principal value of a currency swap is subject to the risk that the other party to the swap will default on its contractual delivery obligations.

A credit default swap may have as reference obligations one or more securities that may, or may not, be currently held by a Fund. The protection “buyer” in a credit default swap is generally obligated to pay the protection “seller” an upfront or a periodic stream of payments over the term of the swap provided that no credit event, such as a default, on a reference obligation has occurred. If a credit event occurs, the seller generally must pay the buyer the “par value” (full notional value) of the swap in exchange for an equal face amount of deliverable obligations of the reference entity described in the swap, or the seller may be required to deliver the related net cash amount, if the swap is cash settled. The Fund may be either the buyer or seller in the transaction. If the Fund is a buyer and no credit event occurs, the Fund may recover nothing if the swap is held through its termination date. However, if a credit event occurs, the buyer generally may elect to receive the full notional value of the swap in exchange for an equal face amount of deliverable obligations of the reference entity whose value may have significantly decreased. As a seller, the Fund generally receives an upfront payment or a rate of income throughout the term of the swap provided that there is no credit event. As the seller, the Fund would effectively add leverage to its portfolio because, in addition to its total net assets, a Fund would be subject to investment exposure on the notional amount of the swap. If a credit event occurs, the value of any deliverable obligation received by the Fund as seller, coupled with the upfront or periodic payments previously received, may be less than the full notional value it pays to the buyer, resulting in a loss of value to the Fund.

To the extent that a Fund’s exposure in a transaction involving a swap or an interest rate floor, cap or collar is covered by the segregation of cash or liquid assets, or is covered by other means in accordance with SEC guidance, the Fund and the Adviser believe that the transactions do not constitute senior securities under the Act and, accordingly, will not treat them as being subject to a Fund’s borrowing restrictions.

The Fund will not enter into any credit default, interest rate, total return or mortgage swap transactions unless the unsecured commercial paper, senior debt or claims-paying ability of the other party thereto is rated investment grade by Standard & Poor’s or Moody’s, or, if unrated by such rating organization, determined to be of comparable quality by the Adviser. If there is a default by the other party to such a transaction, the Fund will have contractual remedies pursuant to the agreements related to the transaction.

The use of credit default, interest rate, mortgage, total return and currency swaps, as well as interest rate caps, floors and collars, is a highly specialized activity which involves investment techniques and risks different from those associated with ordinary portfolio securities transactions. The use of a swap requires an understanding not only of the referenced asset, reference rate, or index but also of the swap itself, without the benefit of observing the performance of the swap under all possible market conditions. If the Adviser is incorrect in its forecasts of market values, credit quality, interest rates and currency exchange rates, the investment performance of the Fund would be less favorable than it would have been if these investment instruments were not used.

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THE FIRST PARAGRAPH UNDER “INVESTMENT INSTRUMENTS AND POLICIES—FOREIGN SECURITIES” IN THE FUND’S STATEMENT OF ADDITIONAL INFORMATION IS AMENDED AND RESTATED AS FOLLOWS:

Foreign Securities. Each of the Large Cap Value, Mid Cap Value, Small Cap Value, All Cap Value, Long/Short Equity, WPG Small Cap Value and WPG Core Bond Funds may invest in securities of foreign issuers either directly or through American Depositary Receipts (“ADRs”) Global Depositary Receipts (“GDRs”), European Depositary Receipts (“EDRs”) or International Depositary Receipts (“IDRs”). The Large Cap Growth Fund may invest in securities of foreign issuers that are traded or denominated in U.S. dollars (including equity securities of foreign issuers trading in U.S. markets) through ADRs, GDRs, EDRs and IDRs. ADRs are securities, typically issued by a U.S. financial institution (a “depository”), that evidence ownership interests in a security or pool of securities issued by a foreign issuer and deposited with the depository. ADRs may be listed on a national securities exchange or may trade in the over-the-counter market. ADR prices are denominated in U.S. dollars; the underlying security may be denominated in a foreign currency. GDRs, EDRs and IDRs are securities that represent ownership interests in a security or pool of securities issued by a non-U.S. or U.S. corporation. Depositary receipts may be available through “sponsored” or “unsponsored” facilities. A sponsored facility is established jointly by the issuer of the security underlying the receipt and the depository, whereas an unsponsored facility is established by the depository without participation by the issuer of the underlying security. Holders of unsponsored depositary receipts generally bear all of the costs of the unsponsored facility. The depository of an unsponsored facility is frequently under no obligation to distribute shareholder communications received from the issuer of the deposited security or to pass through, to the holders of the receipts, voting rights with respect to the deposited securities. The depository of unsponsored depositary receipts may provide less information to receipt holders. Investments in depositary receipts do not eliminate the risks in investing in foreign issuers. The underlying security may be subject to foreign government taxes, which would reduce the yield on such securities.

THE SECTION “INVESTMENT INSTRUMENTS AND POLICIES—FORWARD FOREIGN CURRENCY TRANSACTIONS” IN THE FUND’S STATEMENT OF ADDITIONAL INFORMATION IS AMENDED AND RESTATED AS FOLLOWS:

Forward Foreign Currency Transactions. Each of the WPG Small Cap Value Fund and WPG Core Bond Fund may, to the extent that it invests in foreign securities, enter into forward foreign currency exchange contracts in order to protect against uncertainty in the level of future foreign currency exchange rates. Each Fund will conduct its foreign currency exchange transactions either on a spot (i.e., cash) basis at the spot rate prevailing in the foreign currency exchange market, or through entering into forward contracts to purchase or sell foreign currencies. A forward foreign currency exchange contract involves an obligation to purchase or sell a specific currency at a future date, which may be any fixed number of days (usually less than one year) from the date of the contract agreed upon by the parties, at a price set at the time of the contract. These contracts are traded in the interbank market conducted directly between traders (usually large commercial banks) and their customers. A forward contract generally has no deposit requirement, and no commissions are charged at any stage for trades. Although foreign exchange dealers do not charge a fee for conversion, they do realize a profit based on the difference (the spread) between the price at which they are buying and selling various currencies.

Each Fund is permitted to enter into forward contracts under two circumstances. First, when a Fund enters into a contract for the purchase or sale of a security quoted or denominated in a foreign currency, it may desire to “lock in” the U.S. dollar price of the security. By entering into a forward contract for the purchase or sale, for a fixed number of U.S. dollars, of the amount of foreign currency involved in the underlying security transactions, the Fund will be able to insulate itself from a possible loss resulting from a change in the relationship between the U.S. dollar and the subject foreign currency during the period between the date on which the security is purchased or sold and the date on which payment is made or received.

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Second, when the Adviser believes that the currency of a particular foreign country may suffer a substantial decline against the U.S. dollar, it may cause a Fund to enter a forward contract to sell, for a fixed U.S. dollar amount, the amount of foreign currency approximating the value of some or all of a Fund’s portfolio securities quoted or denominated in such foreign currency. The precise matching of the forward contract amounts and the value of the securities involved will not generally be possible since the future value of such securities in foreign currencies will change as a consequence of market movements in the value of those securities between the date the forward contract is entered into and the date it matures.

Although each Fund has no current intention to do so, it may engage in cross-hedging by using forward contracts in one currency to hedge against fluctuations in the value in securities denominated or quoted in a different currency if the Adviser determines that there is a pattern of correlation between the two currencies. Cross-hedging may also include entering into a forward transaction involving two foreign currencies, using one foreign currency as a proxy for the U.S. dollar to hedge against variations in the other U.S. foreign currency, if the Adviser determines that there is a pattern of correlation between the proxy currency and the U.S. dollar.

A Fund will not enter into forward contracts to sell currency or maintain a net exposure to such contracts if the consummation of such contracts would obligate the Fund to deliver an amount of foreign currency in excess of the value of the Fund’s respective portfolio securities or other assets quoted or denominated in that currency. At the consummation of the forward contract, a Fund may either make delivery of the foreign currency or terminate its contractual obligation by purchasing an offsetting contract obligating it to purchase at the same maturity date, the same amount of such foreign currency. If a Fund chooses to make delivery of foreign currency, it may be required to obtain such delivery through the sale of portfolio securities quoted or denominated in such currency or through conversion of other assets of a Fund into such currency. If a Fund engages in an offsetting transaction, the Fund will realize a gain or a loss to the extent that there has been a change in forward contract prices. Closing purchase transactions with respect to forward contracts are usually effected with the currency trader who is party to the original forward contract.

A Fund’s transactions in forward contracts will be limited to those described above. Of course, a Fund is not required to enter into such transactions with regard to its foreign currency quoted or denominated securities, and a Fund will not do so unless deemed appropriate by the Adviser.

When entering into a forward contract, a Fund will segregate either cash or liquid securities quoted or denominated in any currency in an amount equal to the value of the Fund’s total assets committed to the consummation of forward currency exchange contracts which require the Fund to purchase a foreign currency. If the value of the segregated securities declines, additional cash or securities will be segregated by the Fund on a daily basis so that the value of the segregated securities will equal the amount of the Fund’s commitments with respect to such contracts.

This method of protecting the value of a Fund’s portfolio securities against a decline in the value of a currency does not eliminate fluctuations in the underlying prices of the securities. It simply establishes a rate of exchange which can be achieved at some future point in time. The precise projection of short-term currency market movements is not possible, and short-term hedging provides a means of fixing the U.S. dollar value of only a portion of a Fund’s foreign assets. It also reduces any potential gain which may have otherwise occurred had the currency value increased above the settlement price of the contract.

While a Fund may enter into forward contracts to seek to reduce currency exchange rate risks, transactions in such contracts involve certain other risks. Thus, while a Fund may benefit from such transactions, unanticipated changes in currency prices may result in a poorer overall performance for the Fund than if it had not engaged in any such transactions. Moreover, there may be imperfect correlation between the Fund’s portfolio holdings or securities quoted or denominated in a particular currency and forward contracts entered into by the Fund. Such imperfect correlation may cause the Fund to sustain losses, which will prevent the Fund from achieving a complete hedge, or expose the Fund to the risk of foreign exchange loss.

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Forward contracts are subject to the risks that the counterparty to such contract will default on its obligations. Since a forward foreign currency exchange contract is not guaranteed by an exchange or clearing house, a default on the contract would deprive the Fund of unrealized profits, transaction costs or the benefits of a currency hedge or force the Fund to cover its purchase or sale commitments, if any, at the current market price.

A Fund’s foreign currency transactions (including related options, futures and forward contracts) may be limited by the requirements of Subchapter M of the Internal Revenue Code of 1986, as amended (the “Code”) for qualification as a regulated investment company.

Please retain this Supplement for future reference.

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