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Investor Class Prospectus | Boston Partners All-Cap Value Fund

SUMMARY SECTION — BOSTON PARTNERS ALL-CAP VALUE FUND

Investment Objective

The Fund seeks to provide long-term growth of capital primarily through investment in equity securities.

Current income is a secondary objective.

Expenses and Fees

This table describes the fees and expenses that you may pay if you buy, hold, and sell Investor Class shares of the Fund.

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

Annual Fund Operating Expenses	Investor Class Prospectus Boston Partners All-Cap Value Fund Investor Class
Management Fees	0.70%
Distribution and/or Service (12b-1) Fees	0.25%
Other Expenses	0.12%
Acquired fund fees and expenses	0.01%	[1]
Total Annual Fund Operating Expenses	1.08%
Fee Waivers and/or Expense Reimbursements	(0.03%)	[2]
Total Annual Fund Operating Expenses after Fee Waivers and/or Expense Reimbursements	1.05%

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 that you sell all of your shares at the end of the period. The Example also assumes that your investment has a 5% return each year and that the operating expenses of the Fund remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example	One Year	Three Years	Five Years	Ten Years
Investor Class Prospectus | Boston Partners All-Cap Value Fund | Investor Class | USD ($)	107	287	483	1,048

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 Total annual Fund operating expenses or in the Example, affect the Fund’s performance. During the fiscal year ended August 31, 2019, the portfolio turnover rate for the Fund was 33% of the average value of its portfolio.

Summary of Principal Investment Strategies

The Fund pursues its objective by investing, under normal circumstances, at least 80% of its net assets (including borrowings for investment purposes) in a diversified portfolio consisting primarily of equity securities, such as common stocks of issuers across the capitalization spectrum and identified by the Adviser as having value characteristics.

The Adviser will sell a stock when it no longer meets one or more investment criteria, either through obtaining target value or due to an adverse change in fundamentals or business momentum. Each holding has a target valuation established at purchase, which the Adviser constantly monitors and adjusts as appropriate.

The Adviser examines various factors in determining the value characteristics of such issuers including price to book value ratios and price to earnings ratios. These value characteristics are examined in the context of the issuer’s operating and financial fundamentals, such as return on equity and earnings growth and cash flow. The Adviser selects securities for the Fund based on a continuous study of trends in industries and companies, earnings power and growth and other investment criteria.

The Fund may also invest up to 20% of its total assets in non U.S. dollar denominated securities.

The Fund may invest up to 15% of its net assets in illiquid securities, including securities that are illiquid by virtue of the absence of a readily available market or legal or contractual restrictions on resale.

The Fund may participate as a purchaser in initial public offerings of securities (“IPO”). An IPO is a company’s first offering of stock to the public.

The Fund may invest up to 10% of its net assets in securities that can be converted into common stock, such as certain debt securities and preferred stock.

The Fund may hedge overall portfolio exposure up to 40% of its net assets through the purchase and sale of index and individual put and call options.

In general, the Fund’s investments are broadly diversified over a number of industries and, as a matter of policy, the Fund is limited to investing less than 25% of its total assets in any one industry.

While the Adviser intends to fully invest the Fund’s assets at all times in accordance with the above-mentioned policies, the Fund reserves the right to hold up to 100% of its assets, as a temporary defensive measure, in cash and eligible U.S. dollar-denominated money market instruments and make investments inconsistent with its investment objective. The Adviser will determine when market conditions warrant temporary defensive measures.

Summary of Principal Risks

Risk is inherent in all investing. The value of your investment in the Fund, as well as the amount of return you receive on your investment, may fluctuate significantly from day to day and over time. You may lose part or all of your investment in the Fund or your investment may not perform as well as other similar investments.The Fund’s principal risks are presented in alphabetical order to facilitate finding particular risks and comparing them with other funds. Each risk summarized below is considered a “principal risk” of investing in the Fund, regardless of the order in which it appears. Different risks may be more significant at different times depending on market conditions or other factors.

● Convertible Securities Risk. Securities that can be converted into common stock, such as certain securities and preferred stock, are subject to the usual risks associated with fixed income investments, such as interest rate risk and credit risk. In addition, because they react to changes in the value of the equity securities into which they will convert, convertible securities are also subject to the risks associated with equity securities.

● Cyber Security Risk. Cyber security risk is the risk of an unauthorized breach and access to Fund assets, Fund or customer data (including private shareholder information), or proprietary information, or the risk of an incident occurring that causes the Fund, the investment adviser, custodian, transfer agent, distributor and other service providers and financial intermediaries to suffer data breaches, data corruption or lose operational functionality or prevent Fund investors from purchasing, redeeming or exchanging shares or receiving distributions. The Fund and its investment adviser have limited ability to prevent or mitigate cyber security incidents affecting third-party service providers. Successful cyber-attacks or other cyber-failures or events affecting the Fund or its service providers may adversely impact and cause financial losses to the Fund or its shareholders.

● Foreign Custody Risk. The Fund may hold foreign securities and cash with foreign banks, agents, and securities depositories appointed by the Fund’s custodian (each a “Foreign Custodian”). Some Foreign Custodians may be recently organized or new to the foreign custody business. In some countries, Foreign Custodians may be subject to little or no regulatory oversight over or independent evaluation of their operations. Further, the laws of certain countries may place limitations on the Fund’s ability to recover its assets if a Foreign Custodian enters bankruptcy. Investments in emerging markets may be subject to even greater custody risks than investments in more developed markets. Custody services in emerging market countries are very often undeveloped and may be considerably less well-regulated than in more developed countries, and thus may not afford the same level of investor protection as would apply in developed countries.

● Foreign Securities Risk. International investing is subject to special risks, including, but not limited to, currency exchange rate volatility, political, social or economic instability, and differences in taxation, auditing and other financial practices.

● Illiquid Securities Risk. Investing in illiquid securities is subject to certain risks, such as limitations on resale and uncertainty in determining valuation. Limitations on resale may adversely affect the marketability of portfolio securities and the Fund might be unable to dispose of restricted or other illiquid securities promptly or at reasonable prices and might thereby experience difficulty satisfying redemptions within seven days. The Fund might, in order to dispose of restricted securities, have to register securities resulting in additional expense and delay. Adverse market conditions could impede such a public offering of such securities. Less liquid securities that the Fund may want to invest in may be difficult or impossible to purchase. Federal banking regulations may also cause certain dealers to reduce their inventories of certain securities, which may further decrease the Fund’s ability to buy or sell such securities.

● IPO Risk. IPO risk is the risk that the market value of IPO shares will fluctuate considerably due to certain factors, such as the absence of a prior public market, unseasoned trading, the small number of shares available for trading and limited information about the issuer. The purchase of IPO shares may involve high transaction costs. IPO shares are subject to market risk and liquidity risk. When the Fund’s asset base is small, a significant portion of the Fund’s performance could be attributable to investments in IPOs, because such investments would have a magnified impact on the Fund. As the Fund’s assets grow, the effect of the Fund’s investments in IPOs on the Fund’s performance probably will decline, which could reduce the Fund’s performance. Because of the price volatility of IPO shares, the Fund may choose to hold IPO shares for a very short period of time. This may increase the turnover of the Fund’s portfolio and may lead to increased expenses to the Fund, such as commissions and transaction costs. In addition, the Adviser cannot guarantee continued access to IPOs.

● Management Risk. The Fund is subject to the risk of poor stock selection. In other words, the individual stocks in the Fund may not perform as well as expected, and/or the Fund’s portfolio management practices do not work to achieve their desired result.

● Market Risk. The net asset value (“NAV”) of the Fund will change with changes in the market value of its portfolio positions. Investors may lose money. Although the Fund will invest in stocks the Adviser believes to be undervalued, there is no guarantee that the prices of these stocks will not move even lower.

● Options Risk. An option is a type of derivative instrument that gives the holder the right (but not the obligation) to buy (a “call”) or sell (a “put”) an asset in the near future at an agreed upon price prior to the expiration date of the option. The Fund may “cover” a call option by owning the security underlying the option or through other means. The value of options can be highly volatile, and their use can result in loss if the Adviser is incorrect in its expectation of price fluctuations.

● Small/Mid-Cap Companies Risk. Investing in securities of companies with micro, small or mid-sized capitalizations tends to be riskier than investing in securities of companies with large capitalizations. Securities of companies with micro, small and mid-sized capitalizations tend to be more volatile than those of large cap companies and, on occasion, may fluctuate in the opposite direction of large cap company securities or the broader stock market averages.

The small capitalization equity securities in which the Fund invests may be traded only in the over-the- counter market or on a regional securities exchange, may be listed only in the quotation service commonly known as the “pink sheets,” and may not be traded every day or in the volume typical of trading on a national securities exchange. These securities may also be subject to wide fluctuations in market value. The trading market for any given small capitalization equity security may be sufficiently small as to make it difficult for the Fund to dispose of a substantial block of such securities. The sale by the Fund of portfolio securities to meet redemptions may require the Fund to sell its small capitalization securities at a discount from market prices or during periods when, in the Adviser’s judgment, such sale is not desirable. Moreover, the lack of an efficient market for these securities may make them difficult to value.

Performance Information

The bar chart and table below illustrate the long-term performance of the Boston Partners All-Cap Value Fund’s Investor Class. The bar chart below shows you how the performance of the Fund’s Investor Class has varied year by year and provides some indication of the risks of investing in the Fund. The bar chart assumes reinvestment of dividends and distributions. As with all such investments, past performance (before and after taxes) is not an indication of future results. Performance reflects fee waivers in effect. If fee waivers were not in place, the Fund’s performance would be reduced. Updated performance information is available at www.boston-partners.com or 1-888-261-4073.

Total Returns for the Calendar Years Ended December 31

Best and Worst Quarterly Performance (for the periods reflected in the chart above):

Best Quarter:	13.26% (quarter ended December 31, 2011)
Worst Quarter:	-17.62% (quarter ended September 30, 2011)

Average Annual Total Returns for the Periods Ended December 31, 2019

The table below compares the average annual total returns for the Fund’s Investor Class both before and after taxes for the past calendar year, past five calendar years and past ten calendar years to the average annual total returns of a broad-based securities market index for the same periods.

Average Annual Total Returns - Investor Class Prospectus - Boston Partners All-Cap Value Fund		1 Year	5 Years	10 Years
Investor Class		27.54%	8.75%	11.78%
Investor Class | After Taxes on Distributions	[1]	26.84%	7.61%	10.75%
Investor Class | After Taxes on Distributions and Sales		16.79%	6.71%	9.56%
Russell 3000® Value Index (reflects no deduction for fees, expenses or taxes)		26.26%	8.20%	11.71%

[1] Acquired fund fees and expenses are indirect fees and expenses that the Fund incurs from investing in the shares of other mutual funds, including money market funds and exchange-traded funds. Please note that the amount of Total annual Fund operating expenses and Total annual Fund operating expenses after fee waiver and/or expense reimbursement shown in the above table will differ from the "Financial Highlights" section of the prospectus, which reflects the operating expenses of the Fund and does not include indirect expenses such as acquired fund fees and expenses.

[2] The Fund's investment adviser, Boston Partners Global Investors, Inc. (the "Adviser"), has contractually agreed to waive all or a portion of its advisory fee and/or reimburse expenses in an aggregate amount equal to the amount by which the Total annual Fund operating expenses (excluding certain items discussed below) for the Fund's Investor Class shares exceeds 1.05% of the average daily net assets attributable to the Fund's Investor Class shares. In determining the Adviser's obligation to waive advisory fees and/or reimburse expenses, the following expenses are not taken into account and could cause net Total annual Fund operating expenses to exceed 1.05%: short sale dividend expenses, brokerage commissions, extraordinary items, interest or taxes. This contractual limitation is in effect until February 28, 2021 and may not be terminated without the approval of the Board of Directors of The RBB Fund, Inc. If at any time the Fund's Total annual fund operating expenses (not including short sale dividend expense, brokerage commissions, extraordinary items, interest or taxes) for a year are less than 1.05% or the expense cap then in effect, whichever is less, the Adviser is entitled to reimbursement by the Fund of the advisory fees forgone and other payments remitted by the Adviser to the Fund within three years from the date on which such waiver or reimbursement was made, provided such reimbursement does not cause the Fund to exceed expense limitations that were in effect at the time of the waiver or reimbursement.

[1] 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 Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.