MassMutual Select Funds

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MassMutual

Select Funds

Prospectus Inside

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MASSMUTUAL SELECT FUNDS

This Prospectus describes the following Funds:

Fund Name Class I Class R5

Service Class

Administrative

Class Class A Class R4 Class R3 MassMutual Select Total Return

Bond Fund MSPZX MSPSX MSPHX MSPLX MPTRX MSPGX MSPNX

MassMutual Select Strategic Bond Fund MSBZX MBSSX MBSYX MSBLX MSBAX MSBRX MSBNX

MassMutual Select BlackRock Global

Allocation Fund MGJIX MGSSX MGSYX MGSLX MGJAX MGJFX MGJRX

MassMutual Select Diversified

Value Fund MDDIX MDVSX MDVYX MDDLX MDDAX MDDRX MDVNX

MassMutual Select Fundamental

Value Fund MFUZX MVUSX MFUYX MFULX MFUAX MFUFX MFUNX

MassMutual Select Large Cap

Value Fund MLVZX MLVSX MMLYX MLVLX MMLAX MLVFX MLVNX

MM S&P 500®_{Index Fund} _MMIZX _MIEZX _MMIEX _MIEYX _MMFFX _MIEAX _MMINX

MassMutual Select Focused Value Fund MFVZX MFVSX MMFYX MMFVX MFVAX MFVFX MFVNX

MassMutual Select Fundamental

Growth Fund MOTZX MOTCX MOTYX MOTLX MOTAX MFGFX MOTNX

MassMutual Select Blue Chip

Growth Fund MBCZX MBCSX MBCYX MBCLX MBCGX MBGFX MBCNX

MassMutual Select Growth

Opportunities Fund MMAZX MGRSX MAGYX MAGLX MMAAX MMGFX MMANX

MassMutual Select Mid-Cap Value Fund MLUZX MLUSX MLUYX MLULX MLUAX MLUFX MLUNX

MassMutual Select Small Cap Value

Equity Fund MMQIX MMQSX MMQYX MMQLX MMQAX MMQFX MMQTX

MassMutual Select Small Company

Value Fund MSVZX MSVSX MMVYX MMYLX MMYAX MMVFX MSVNX

MM S&P®_{Mid Cap Index Fund} _MDKZX _MDKIX _MDKSX _MDKYX _MDKAX _MDKFX _MDKTX

MM Russell 2000®_{Small Cap}

Index Fund MCJZX MCJIX MCJSX MCJYX MCJAX MCJFX MCJTX

MassMutual Select Mid Cap Growth

Equity II Fund MEFZX MGRFX MEFYX MMELX MEFAX MEFFX MEFNX

MassMutual Select Small Cap Growth

Equity Fund MSGZX MSGSX MSCYX MSGLX MMGEX MSERX MSGNX

MassMutual Select Small Company

Growth Fund MRWIX MSCSX MMCYX MMCLX MRWAX MRWFX MRWTX

MassMutual Select Diversified

International Fund MMZIX MMZSX MMZYX MMZLX MMZAX MMZFX MMZTX

MM MSCI EAFE®_{International}

Index Fund MKRZX MKRIX MKRSX MKRYX MKRAX MKRFX MKRTX

MassMutual Select Overseas Fund MOSZX MOSSX MOSYX MOSLX MOSAX MOSFX MOSNX

The Securities and Exchange Commission has not approved or disapproved these securities or passed upon the adequacy of this Prospectus. Any statement to the contrary is a crime.

PROSPECTUS April 1, 2015

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MASSMUTUAL SELECT FUNDS MassMutual Select Small Company Value Fund

Supplement dated December 14, 2015 to the Prospectus dated April 1, 2015 and the Summary Prospectus dated April 1, 2015

This supplement provides new and additional information beyond that contained in the Prospectus and Summary Prospectus and any previous supplements. It should be retained and read in conjunction with the Prospectus and Summary Prospectus and any previous supplements.

The following information pertains to theSmall Company Value Fund:

Effective immediately, the information forLawrence R. Creaturaunder the headingPortfolio Managersin the section titledManagement(page 69 in the Prospectus) and under the headingSubadvisers and Portfolio Managersin the section titledManagement of the Fundson page 125 of the Prospectus is hereby deleted.

PLEASE RETAIN THIS SUPPLEMENT FOR FUTURE REFERENCE

B3001M-15-09 SCV 15-01

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MASSMUTUAL SELECT FUNDS MassMutual Select Small Company Growth Fund

Supplement dated October 1, 2015 to the Prospectus dated April 1, 2015 and the Summary Prospectus dated April 1, 2015

This supplement provides new and additional information beyond that contained in the Prospectus and Summary Prospectus and any previous supplements. It should be retained and read in conjunction with the Prospectus and Summary Prospectus and any previous supplements.

The following information pertains to theSmall Company Growth Fund:

Effective September 28, 2015 (the “Termination Date”), theSmall Company Growth Fund(the “Fund”) was dissolved pursuant to a Plan of Liquidation and Termination approved by the Board of Trustees of the MassMutual Select Funds. Shareholders of the various classes of shares of the Fund received proceeds in proportion to the number of shares of such class held by each of them on the Termination Date.

B3001M-15-08 SCG 15-03

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MASSMUTUAL SELECT FUNDS Supplement dated September 30, 2015 to the

Prospectus dated April 1, 2015

This supplement provides new and additional information beyond that contained in the Prospectus and any previous supplements. It should be retained and read in conjunction with the Prospectus and any previous supplements.

Effective September 30, 2015, Waddell & Reed Investment Management Company (“Waddell & Reed”) was removed as co-Subadviser to theSmall Cap Growth Equity Fundtherefore all references to Waddell & Reed in the Prospectus are hereby deleted.

Effective immediately, the following information replaces the last sentence in the first paragraph on page 52 underPrincipal Investment Strategiesfor theSelect Growth Opportunities Fund.

Note that although the Fund was originally registered as a non-diversified fund, under a position of the SEC, the Fund is currently required to operate as a diversified fund and will not operate as a non-diversified fund in the future until it obtains any necessary shareholder approval.

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Important Notice Regarding Change in Investment Policy

The 80% test relating the name of the Mid-Cap Value Fund (the “Fund”) to its principal investments, as required by Rule 35d-1 under the Investment Company Act, has been modified as described below. The change will take effect no earlier than 60 days from the date of this supplement as described below.

On or about November 17, 2015, the following information will replace similar information found in the Supplement dated September 9, 2015, which previously replaced the information for theMid-Cap Value Fund found in the first paragraph under the headingPrincipal Investment Strategieson pages 56-57:

The Fund invests primarily in equity securities of mid-capitalization companies that the subadvisers believe are undervalued. Equity securities may include common stocks, preferred stocks, securities convertible into common or preferred stock, stock futures contracts, stock index futures contracts, rights, and warrants. Under normal circumstances, the Fund invests at least 80% of its net assets in the stocks of mid-cap companies. The

subadvisers currently define “mid-cap” companies as those whose market capitalizations at the time of purchase are between $500 million and $40 billion. The Fund typically invests most of its assets in equity securities of U.S. companies, but may gain exposure to non-U.S. issuers, including emerging markets issuers, through the purchase of foreign securities and American Depositary Receipts (“ADRs”). The Fund may also invest a portion of its assets in real estate investment trusts (“REITs”). The Fund may use futures contracts as a substitute for direct investments in equity securities. The Fund may but will not necessarily engage in foreign currency forward contracts to attempt to protect against adverse changes in currency exchange rates. Use of derivatives by the Fund may create investment leverage. The Fund may invest a portion of its assets in debt securities of companies and debt obligations of governments and their agencies, and other similar securities. The Fund may hold a portion of its assets in cash or cash equivalents.

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Effective September 9, 2015, American Century Investment Management, Inc. (“American Century”) replaced NFJ Investment Group LLC (“NFJ”) as a co-subadviser to the Mid-Cap Value Fund.

Effective September 9, 2015, the following information replaces all of the information for the Mid-Cap Value Fund found on pages 56-57 under the heading Principal Investment Strategies:

The Fund invests primarily in equity securities of mid-capitalization companies that the subadvisers believe are undervalued. Equity securities may include common stocks, preferred stocks, securities convertible into common or preferred stock, stock futures contracts, stock index futures contracts, rights, and warrants. Under normal circumstances, the Fund invests at least 80% of its net assets in the stocks of mid-cap companies. The subadvisers currently define “mid-cap” companies as those whose market

capitalizations at the time of purchase are between $500 million and $10 billion or fall within the market capitalization range of companies included in the Russell Midcap Value Index (as of January 31, 2015, between $200 million and $32.48 billion). The Fund typically invests most of its assets in equity securities of U.S. companies, but may gain exposure to non-U.S. issuers, including emerging markets issuers, through the purchase of foreign securities and American Depositary Receipts (“ADRs”). The Fund may also invest a portion of its assets in real estate investment trusts (“REITs”). The Fund may use futures contracts as a substitute for direct investments in equity securities. The Fund may but will not necessarily engage in foreign currency forward contracts to attempt to protect against adverse changes in currency exchange rates. Use of derivatives by the Fund may create investment leverage. The Fund may invest a portion of its assets in debt securities of companies and debt obligations of governments and their agencies, and other similar securities. The Fund may hold a portion of its assets in cash or cash equivalents.

The Fund is managed by two subadvisers, American Century Investment Management, Inc. (“American Century”) and Systematic Financial Management, L.P. (“Systematic”), each being responsible for a portion of the portfolio, but not necessarily equally weighted. In selecting investments for the Fund, American Century seeks to identify stocks of companies that it believes are undervalued at the time of purchase. American Century attempts to purchase the stocks of these undervalued companies and hold each stock until it has returned to favor in the market and the stock’s price has increased to, or is higher than, a level the managers believe more accurately reflects the fair value of the company. Companies may be undervalued due to market declines, poor

economic conditions, actual or anticipated bad news regarding the issuer or its industry, or because they have been overlooked by the market. To identify these companies, American Century looks for companies with earnings, cash flows and/or assets that may not be accurately reflected in the companies’ values, as determined by the managers. The managers also may consider whether the

companies’ securities have a favorable income-paying history and whether income payments are expected to continue or increase. In selecting securities for the Fund, Systematic utilizes a two-prong, bottom-up investment strategy that unifies quantitative screening and fundamental research. Systematic’s security selection process generally favors companies with attractive valuation and positive earnings dynamics, and may consider, among other things, a company’s financial characteristics, market position, industry position, and management.

American Century may sell a stock from the Fund if, for example, in its judgment, a stock no longer meets its valuation criteria, a stock’s risk parameters outweigh its return opportunity, more attractive alternatives are identified, or specific events alter a stock’s prospects. Systematic generally may consider selling a stock for the Fund if, for example, in its judgment, the stock’s price has appreciated to a level that Systematic considers to be the stock’s fair value, its analysis leads Systematic to anticipate downward earnings revisions for a company, a company experiences an unexpected earnings announcement, or Systematic identifies other investment opportunities that it believes to be more attractive.

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The Fund expects that it will engage in active and frequent trading and so will typically have a relatively high portfolio turnover rate.

Effective September 9, 2015, the following information supplements the information for the Mid-Cap Value Fund found on pages 57-58 under the heading Principal Risks:

Credit Risk Credit risk is the risk that an issuer, guarantor, or liquidity provider of a fixed income security held by the Fund may be unable or unwilling, or may be perceived (whether by market participants, ratings agencies, pricing services or otherwise) as unable or unwilling, to make timely principal and/or interest payments, or to otherwise honor its obligations. The Fund may also be exposed to the credit risk of its counterparty to repurchase agreements, reverse repurchase agreements, swap transactions, and other derivatives transactions. The value of such transactions to the Fund will depend on the willingness and ability of the counterparty to perform its obligations, including among other things the obligation to return collateral or margin to the Fund.

Derivatives Risk Derivatives can be highly volatile and involve risks different from, and potentially greater than, direct investments, including risks of imperfect correlation between the value of derivatives and underlying assets, counterparty default, potential losses that partially or completely offset gains, and illiquidity. Derivatives can create investment leverage. Gains or losses from derivatives can be substantially greater than the derivatives’ original cost and can sometimes be unlimited. If the value of a derivative does not correlate well with the particular market or asset class the derivative is designed to provide exposure to, the derivative may not have the effect anticipated. Derivatives can also reduce the opportunity for gains or result in losses by offsetting positive returns in other investments. Many derivatives are traded in the over-the-counter market and not on exchanges.

Fixed Income Securities Risk The values of fixed income securities typically will decline during periods of rising interest rates, and can also decline in response to changes in the financial condition of the issuer, borrower, counterparty, or underlying collateral assets, or changes in market, economic, industry, political, and regulatory conditions affecting a particular type of security or issuer or fixed income securities generally. Certain events, such as market or economic developments, regulatory or government actions, natural disasters, terrorist attacks, war, and other geopolitical events can have a dramatic adverse effect on the debt market and the overall liquidity of the market for fixed income securities. During those periods, the Fund may

experience high levels of shareholder redemptions, and may have to sell securities at times when the Fund would otherwise not do so, and potentially at unfavorable prices. Certain securities may be difficult to value during such periods. Fixed income securities are subject to interest rate risk (the risk that the value of a fixed income security will fall when interest rates rise), extension risk (the risk that the average life of a security will be extended through a slowing of principal payments), prepayment risk (the risk that a security will be prepaid and the Fund will be required to reinvest at a less favorable rate), and credit risk. These risks may be heightened due to the current historically low interest rate environment.

Sovereign Debt Obligations Risk Investments in debt securities issued by governments or by government agencies and instrumentalities involve the risk that the governmental entities responsible for repayment may be unable or unwilling to pay interest and repay principal when due. Many sovereign debt obligations may be rated below investment grade (“junk” or “high yield” bonds). Any restructuring of a sovereign debt obligation held by the Fund will likely have a significant adverse effect on the value of the obligation. In the event of default of sovereign debt, the Fund may be unable to pursue legal action against the sovereign issuer or to realize on collateral securing the debt.

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Effective September 9, 2015, the following information replaces similar information for the Mid Cap Value Fund found on page 59 under the headings Subadvisers and Portfolio Managers in the section titled Management:

Subadvisers: American Century Investment Management, Inc. Systematic Financial Management, L.P.

Portfolio Managers:

Phillip N. Davidson, CFA is Chief Investment Officer – U.S. Value Equity, Senior Vice President, and Senior Portfolio Manager at American Century. He has managed the Fund since September 2015.

Michael Liss, CFA is a Vice President and Senior Portfolio Manager at American Century. He has managed the Fund since September 2015.

Kevin Toney, CFA is a Senior Vice President and Senior Portfolio Manager at American Century. He has managed the Fund since September 2015.

Brian Woglom, CFA is a Vice President and Portfolio Manager at American Century. He has managed the Fund since September 2015.

Ronald M. Mushock, CFA is a Managing Partner at Systematic and is the Lead Portfolio Manager of Systematic’s Mid Cap Portfolios. He has managed the Fund since June 2009.

D. Kevin McCreesh, CFA is a Managing Partner at Systematic and is Systematic’s Chief Investment Officer. He has managed the Fund since June 2009.

Effective September 9, 2015, the following information replaces the information for NFJ Investment Group LLC found on pages 130-131 under the heading Subadvisers and Portfolio Managers in the section titled Management of the Funds:

American Century Investment Management, Inc. (“American Century”), located at 4500 Main Street, Kansas City, Missouri 64111, manages the investments of the Mid-Cap Value Fund. American Century is a privately held subsidiary of American Century Companies, Inc. As of August 31, 2015, American Century had approximately $144.8 billion in total assets under management. American Century replaced NFJ Investment Group LLC as a co-subadviser of the Mid-Cap Value Fund on September 9, 2015. NFJ Investment Group LLC had been a co-subadviser of the Mid-Cap Value Fund since March 2010.

Phillip N. Davidson, CFA

is a portfolio manager of a portion of the Mid-Cap Value Fund, which is managed on a team basis. He is jointly and

primarily responsible for the day-to-day management of the Fund. Mr. Davidson is the Chief Investment Officer – U.S. Value Equity, Senior Vice President and Senior Portfolio Manager for American Century. He joined American Century in 1993 as a portfolio manager.

Michael Liss, CFA

primarily responsible for the day-to-day management of the Fund. Mr. Liss is a Vice President and Senior Portfolio Manager for American Century. Mr. Liss joined American Century in 1998 and became a portfolio manager in 2004.

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Kevin Toney, CFA

is a portfolio manager of a portion of the Mid-Cap Value Fund, which is managed on a team basis. He is jointly and primarily responsible for the day-to-day management of the Fund. Mr. Toney is a Senior Vice President and Senior Portfolio Manager for American Century. Mr. Toney joined American Century in 1999 as an investment analyst and became a portfolio manager in 2006.

Brian Woglom, CFA

primarily responsible for the day-to-day management of the Fund. Mr. Woglom is a Vice President and Portfolio Manager for American Century. Mr. Woglom joined American Century in 2005 as an investment analyst and became a portfolio manager in 2012.

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Supplement dated August 31, 2015 to the Prospectus dated April 1, 2015 and the Summary Prospectus dated April 1, 2015

This supplement provides new and additional information beyond that contained in the Prospectus and Summary Prospectus, and any previous supplements. It should be retained and read in conjunction with the Prospectus, Summary Prospectus, and any previous supplements.

The following information pertains to theSmall Company Growth Fund:

Effective September 1, 2015, Montibus Capital Management LLC (“Montibus”) will no longer act as subadviser to theSmall Company Growth Fund. In order to achieve its investment objective until it dissolves on or about September 28, 2015, theSmall Company Growth Fund’sprincipal investment strategy will be to invest in one or more Exchange-Traded Funds (“ETFs”) that seek to replicate the investment performance of theSmall Company Growth Fund’sbenchmark index, the Russell 2000 Growth Index. Effective September 1, 2015, MML Investment Advisers, LLC, theSmall Company Growth Fund’sinvestment adviser, will waive the portion of the Fund’s investment management fees that it otherwise would have paid to Montibus.

B3001M-15-04 SCG-15-02

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MASSMUTUAL SELECT FUNDS

MassMutual Select Small Cap Growth Equity Fund Supplement dated July 10, 2015 to the

This supplement provides new and additional information beyond that contained in the Prospectus, and any previous supplements. It should be retained and read in conjunction with the Prospectus, and any previous supplements.

Effective July 7, 2015, OFI Global Institutional, Inc. (“OFI Global”) replaced Montibus Capital Management LLC (“Montibus”) as subadviser to theSmall Cap Growth Equity Fund.

The following information replaces the information found in the second paragraph underPrincipal Investment Strategieson page 83 for theSmall Cap Growth Equity Fund:

The Fund is managed by three subadvisers,Wellington Management Company LLP(“Wellington Management”),

Waddell & Reed Investment Management Company(“Waddell & Reed”), andOFI Global Institutional, Inc.

(“OFI Global”), each being responsible for a portion of the portfolio, but not necessarily equally weighted. Each subadviser employs a growth-based investment approach and may perform a number of analyses in considering whether to buy or sell a security for the Fund. Wellington Management and Waddell & Reed use a combination of fundamental and quantitative analyses to identify small-cap companies that it believes are experiencing or will experience rapid earnings or revenue growth and OFI Global uses fundamental research to select securities for the Fund’s portfolio. A subadviser may consider selling a security for the Fund if, for example, in its judgment, target prices are reached, future upside potential is limited, company fundamentals are no longer attractive, superior purchase candidates are identified, or market capitalization ceilings are exceeded.

The following information supplements the information found underPrincipal Riskson pages 83 and 84 for theSmall Cap Growth Equity Fund:

Sector RiskThe Fund may allocate more of its assets to certain economic, market, or industry sectors than to others. This could increase the volatility of the Fund’s portfolio, and the Fund’s performance may be more susceptible to developments affecting issuers in those sectors than if the Fund invested more broadly.

The information under the headingSubadvisersand under the headingPortfolio Managersrelating to the Small Cap Growth Equity Fundfound on page 85 in the section titledManagementis hereby replaced by the following information:

Subadvisers:Wellington Management Company LLP Waddell & Reed Investment Management Company OFI Global Institutional, Inc.

Kenneth L. Abramsis a Senior Managing Director and Equity Portfolio Manager at Wellington Management. He has managed the Fund since November 2001.

Daniel J. Fitzpatrick, CFAis a Managing Director and Equity Research Analyst at Wellington Management. He has managed the Fund since November 2001.

Steven C. Angeli, CFAis a Senior Managing Director and Equity Portfolio Manager at Wellington Management. He has managed the Fund since April 2004.

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Mario E. Abularach, CFAis a Senior Managing Director and Equity Research Analyst at Wellington Management. He has managed the Fund since April 2006.

Stephen Mortimeris a Senior Managing Director and Equity Portfolio Manager at Wellington Management. He has managed the Fund since April 2006.

Gilbert C. Scottis a Senior Vice President and Portfolio Manager at Waddell & Reed. He has managed the Fund since April 2010.

Ronald Zibelli, Jr., CFAis a Senior Portfolio Manager at OFI Global. He has managed the Fund since July 2015.

Ash Shah, CFAis a Portfolio Manager at OFI Global. He has managed the Fund since July 2015.

The following information replaces the information forMontibus Capital Management LLCfound under the headingSubadvisers and Portfolio Managerson page 130 in the section titledManagement of the Funds:

Montibus Capital Management LLC(“Montibus”), a Delaware limited liability company with principal offices located at 805 SW Broadway, Portland, Oregon 97205, manages the investments of theSmall Company Growth Fund. Montibus is an indirect subsidiary of Stifel Financial Corp. Montibus was founded in 2006. As of December 31, 2014, Montibus managed approximately $982 million in U.S. small and small/mid cap growth portfolios.

Kenneth A. Korngiebel, CFA

is the portfolio manager of theSmall Company Growth Fund. Mr. Korngiebel is Montibus’s Chief Investment Officer and Lead Portfolio Manager. He has been an investment professional since 1996, and joined Montibus at its inception in 2006.

The following information supplements the information found under the headingSubadvisers and Portfolio Managerson pages 122-135 in the section titledManagement of the Funds:

OFI Global Institutional, Inc.(“OFI Global”), located at 225 Liberty Street, 11th Floor, New York, NY 10281, manages a portion of the investments of theSmall Cap Growth Equity Fund. OFI Global is a wholly owned subsidiary of OppenheimerFunds, Inc. (“OFI”), a majority owned, indirect subsidiary of MassMutual. As of May 31, 2015, OFI Global had approximately $8.1 billion in assets under management.

Ronald Zibelli, Jr., CFA

is a co-portfolio manager of a portion of theSmall Cap Growth Equity Fund. Mr. Zibelli has been a Senior Portfolio Manager at OFI Global since May 2006. Prior to joining OFI Global, he spent six years at Merrill Lynch Investment Managers, during which time he was a Managing Director and Small Cap Growth Team Leader, responsible for managing 11 portfolios. Prior to joining Merrill Lynch Investment Managers, Mr. Zibelli spent 12 years with Chase Manhattan Bank, including two years as Senior Portfolio Manager (U.S. Small Cap Equity) at Chase Asset Management.

Ash Shah, CFA

is a co-portfolio manager of a portion of theSmall Cap Growth Equity Fund. Mr. Shah has been a Senior Portfolio Manager at OFI Global since February 2014. Mr. Shah was a Senior Research Analyst of OFI Global from February 2006 to February 2014. Prior to joining OFI Global, Mr. Shah was a Vice President and Senior Analyst with Merrill Lynch Investment Managers. Prior to that, he was a Vice President and Senior Analyst for BlackRock Financial Management.

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Supplement dated July 1, 2015 to the Prospectus dated April 1, 2015 and the Summary Prospectus dated April 1, 2015

This supplement provides new and additional information beyond that contained in the Prospectus and Summary Prospectus, and any previous supplements. It should be retained and read in conjunction with the Prospectus and Summary Prospectus, and any previous supplements.

The following information pertains to theSmall Company Growth Fund:

The Board of Trustees of the MassMutual Select Funds has approved a Plan of Liquidation and Termination pursuant to which it is expected that theSmall Company Growth Fund(the “Fund”) will be dissolved.

Effective on or about September 28, 2015 (the “Termination Date”), shareholders of the various classes of shares of the Fund will receive proceeds in proportion to the number of shares of such class held by each of them on the Termination Date.

Please note that prior to the Termination Date, the Fund may hold most or all of its assets in cash or cash equivalents and therefore may not be able to meet its investment objective.

B3001M-15-02 SCG-15-01

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MASSMUTUAL SELECT FUNDS Supplement dated May 12, 2015 to the

This supplement provides new and additional information beyond that contained in the Prospectus. It should be retained and read in conjunction with the Prospectus.

Effective immediately, the following information under the headingAnnual Fund Operating Expenses found on page 48 in the section titledFees and Expenses of the Fundrelating to theBlue Chip Growth Fundis hereby replaced by the following information:

Annual Fund Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) Class I Class R5 Service Class Adminis-trative

Class Class A Class R4 Class R3

Management Fees .63% .63% .63% .63% .63% .63% .63%

Distribution and Service (Rule 12b-1) Fees None None None None .25% .25% .50%

Other Expenses(1) _.04% _.14% _.24% _.34% _.34% _.24% _.24%

Total Annual Fund Operating Expenses .67% .77% .87% .97% 1.22% 1.12% 1.37%

(1)_{Other Expenses have been restated to reflect current fees.}

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. It assumes that you invest $10,000 in each share class of the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. For Class A shares, the example includes the initial sales charge. The example also assumes that your investment earns a 5% return each year and that the Fund’s operating expenses are exactly as described in the preceding table. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

1 Year 3 Years 5 Years 10 Years

Class I $ 68 $214 $ 373 $ 835 Class R5 $ 79 $246 $ 428 $ 954 Service Class $ 89 $278 $ 482 $1,073 Administrative Class $ 99 $309 $ 536 $1,190 Class A $692 $940 $1,207 $1,967 Class R4 $114 $356 $ 617 $1,363 Class R3 $139 $434 $ 750 $1,646

Effective immediately, the following information replaces similar information relating to theBlue Chip Growth Fundfound under the headingSubadvisers and Portfolio Managerson page 132 in the section titled Management of the Funds:

T. Rowe Price Associates, Inc.(“T. Rowe Price”), located at 100 East Pratt Street, Baltimore, Maryland 21202, manages a portion of the portfolio of theBlue Chip Growth Fund,Mid Cap Growth Equity II Fund, andSmall Company Value Fund. T. Rowe Price, a wholly-owned subsidiary of T. Rowe Price Group, Inc., a publicly-traded financial services holding company, has been managing assets since 1937. As of December 31, 2014, T. Rowe Price and its affiliates had approximately $746.8 billion in assets under management.

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Larry J. Puglia, CFA, CPA

is the portfolio manager of a portion of theBlue Chip Growth Fund. Mr. Puglia, investment advisory committee chairman of the T. Rowe Price Blue Chip Growth Fund, has day-to-day responsibility for managing the portfolio and works with the committee in developing and executing the portfolio’s investment program. He is a Vice President of T. Rowe Price. Mr. Puglia joined T. Rowe Price in 1990.

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MassMutual Select Total Return Bond Fund

INVESTMENT OBJECTIVE

This Fund seeks maximum total return, consistent with preservation of capital and prudent investment management.

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. For Class A shares, you may qualify for sales charge discounts if you invest, or agree to invest in the future, at least $25,000 in MassMutual funds. More information about these and other discounts is available in the section titledSales Charges by Class

beginning on page 137 of the Fund’s Prospectus or from your financial professional.

Shareholder Fees(fees paid directly from your investment) Class I Class R5 Service Class Admini-strative Class Class A Class R4 Class R3 Maximum Sales Charge (Load) Imposed on Purchases (as a % of

offering price) None None None None 4.75% None None

Maximum Deferred Sales Charge (Load) (as a % of the lower of the original offering price or redemption

proceeds) None None None None None None None

Annual Fund Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) Class I Class R5 Service Class Admini-strative Class Class A Class R4 Class R3 Management Fees .35% .35% .35% .35% .35% .35% .35% Distribution and Service (Rule 12b-1)

Fees None None None None .25% .25% .50%

Other Expenses(1)_{.06% .16%} _.26% _.36% _{.36% .26% .26%} Total Annual Fund Operating Expenses .41% .51% .61% .71% .96% .86% 1.11% Fee Waiver (.05%)(.05%) (.05%) (.05%) (.05%)(.05%) (.05%) Total Annual Fund Operating Expenses after Fee Waiver(2) _{.36% .46%} _.56% _.66% _{.91% .81% 1.06%}

(1) Other Expenses have been restated to reflect current fees. (2) The expenses in the above table reflect a written agreement by

MML Advisers to waive .05% of the management fees of the Fund through March 31, 2016. The agreement can only be terminated by mutual consent of the Board of Trustees on behalf of the Fund and MML Advisers.

Example

1 Year 3 Years 5 Years 10 Years

Class I $ 37 $127 $225 $ 513 Class R5 $ 47 $159 $280 $ 636 Service Class $ 57 $190 $335 $ 757 Administrative Class $ 67 $222 $390 $ 878 Class A $563 $762 $976 $1,593 Class R4 $ 83 $269 $472 $1,056 Class R3 $108 $348 $607 $1,347 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 453% of the average value of its portfolio. INVESTMENTS, RISKS, AND PERFORMANCE Principal Investment Strategies

Under normal circumstances, the Fund invests at least 80% of its net assets in a diversified portfolio of investment grade fixed income securities (rated Baa3 or higher by Moody’s, BBB- or higher by Standard & Poor’s, BBB- or higher by Fitch, or A-2 by S&P, P-2 by Moody’s, or F-2 by Fitch for short-term debt obligations, or, if unrated, determined by the Fund’s subadviser,Metropolitan West Asset Management,

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LLC(“MetWest”), to be of comparable quality). These typically include bonds, notes, collateralized bond obligations, collateralized debt obligations, mortgage-related and asset-backed securities, municipal securities, private placements, and securities subject to legal restrictions on resale pursuant to Rule 144A. These investments may have interest rates that are fixed, variable, or floating. The Fund invests in securities of varying maturities issued by domestic and foreign corporations and

governments (and their agencies and

instrumentalities). The subadviser focuses the Fund’s portfolio holdings in areas of the bond market (based on quality, sector, coupon, or maturity) that the subadviser believes to be relatively undervalued. The Fund may invest up to 20% of its net assets in below investment grade debt securities (“junk” or “high yield” bonds), including securities in default and bank loans. In the event that a security is downgraded after its purchase by the Fund, the Fund may continue to hold the security if the Fund’s subadviser considers doing so would be consistent with the Fund’s investment objective.

The Fund may invest up to 25% of its total assets in foreign securities that are denominated in U.S. dollars. The Fund may also invest up to 15% of its total assets in foreign securities that are not

denominated in U.S. dollars and up to 10% of its total assets in emerging market foreign securities.

The Fund may but will not necessarily engage in foreign currency forward transactions to take long or short positions in foreign currencies in order to enhance the Fund’s investment return or to attempt to protect against adverse changes in currency exchange rates. In pursuing its investment objective, the Fund may (but is not obligated to) use a wide variety of exchange-traded and over-the-counter derivatives, including options, futures contracts, and swap contracts for hedging or investment purposes as a substitute for investing directly in securities or to adjust various portfolio characteristics, including the duration (interest rate volatility) of the Fund’s portfolio. Use of derivatives by the Fund may create investment leverage.

The Fund may purchase and sell securities on a when-issued, delayed delivery, or forward

commitment basis. The Fund may normally short sell up to 25% of the value of its total assets for hedging or investment purposes.

The Fund may also invest in money market securities, including commercial paper. The Fund

may enter into repurchase agreement transactions. The Fund may hold a portion of its assets in cash or cash equivalents. The Fund may enter into dollar roll or reverse repurchase agreement transactions. MetWest intends for the Fund’s portfolio duration to be between two to eight years. The dollar-weighted average maturity of the Fund’s portfolio is expected to range from two to fifteen years. Duration measures the price sensitivity of a bond to changes in interest rates. Duration is the dollar weighted average time to maturity of a bond utilizing the present value of all future cash flows.

MetWest employs a value-oriented fixed income management philosophy with a goal of consistently outperforming the portfolio benchmark while maintaining volatility similar to the benchmark. The investment process is predicated on a long-term economic outlook, which is determined by the investment team on a quarterly basis and is reviewed constantly. Investments are characterized by

diversification among the sectors of the fixed income marketplace. The investment management team seeks to achieve the desired outperformance through the measured and disciplined application of five fixed income management strategies which include duration management, yield curve positioning, sector allocation, security selection, and opportunistic execution.

The first three strategies are top-down in orientation and start with a decision of where within the plus-or-minus one year range around the benchmark the duration should be established. Then comes a determination of how the overall average duration is to be effected – with a concentration of intermediate maturity issues or a combination of long- and short-term issues. The relative value decision regarding where to overweight/

underweight sectors, including governments, agencies, corporates, mortgages, or asset-backed securities, is dependent on the current market environment. Bottom-up security selection involves the day-to-day

fundamental analysis of available bond market opportunities, while execution is characterized by the aggressive and informed negotiation of the prices at which transactions take place.

The Fund expects that it will engage in active and frequent trading and so will typically have a relatively high portfolio turnover rate. Principal Risks

The following are the Principal Risks of the Fund. The value of your investment in the Fund could go

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down as well as up. You can lose money by investing in the Fund.

Bank Loans RiskBank loans in which the Fund may invest have similar risks to below investment grade debt securities. Changes in the financial condition of the borrower or economic conditions or other circumstances may reduce the capacity of the borrower to make principal and interest payments on such instruments and may lead to defaults. Senior secured bank loans are typically supported by collateral; however the value of the collateral may be insufficient to cover the amount owed to the Fund, or the Fund may be prevented or delayed from realizing on the collateral. If the Fund relies on a third party to administer a loan, the Fund is subject to the risk that the third party will fail to perform its obligations. In addition, if the Fund holds only a participation interest in a loan made by a third party, the Fund’s receipt of payments on the loan will depend on the third party’s willingness and ability to make those payments to the Fund. The settlement time for certain loans is longer than the settlement time for many other types of investments, and the Fund may not receive the payment for a loan sold by it until well after the sale; that cash would be unavailable for payment of redemption proceeds or for reinvestment.

Below Investment Grade Debt Securities Risk

Below investment grade debt securities, commonly known as “junk” or “high yield” bonds, have speculative characteristics and involve greater volatility of price and yield, greater risk of loss of principal and interest, and generally reflect a greater possibility of an adverse change in financial

condition that could affect an issuer’s ability to honor its obligations.

Cash Position RiskIf the Fund holds a significant portion of its assets in cash or cash equivalents, its investment returns may be adversely affected and the Fund may not achieve its investment objective.

Credit RiskCredit risk is the risk that an issuer, guarantor, or liquidity provider of a fixed income security held by the Fund may be unable or unwilling, or may be perceived (whether by market participants, ratings agencies, pricing services or otherwise) as unable or unwilling, to make timely principal and/or interest payments, or to otherwise honor its obligations. The Fund may also be exposed to the credit risk of its counterparty to repurchase agreements, reverse repurchase agreements, swap transactions, and other derivatives transactions. The

value of such transactions to the Fund will depend on the willingness and ability of the counterparty to perform its obligations, including among other things the obligation to return collateral or margin to the Fund.

Defaulted Securities RiskBecause the issuer of such securities is in default and is likely to be in distressed financial condition, repayment of defaulted securities and obligations of distressed issuers (including insolvent issuers or issuers in payment or covenant default, in workout or restructuring, or in bankruptcy or insolvency proceedings) is uncertain.

Derivatives RiskDerivatives can be highly volatile and involve risks different from, and potentially greater than, direct investments, including risks of imperfect correlation between the value of derivatives and underlying assets, counterparty default, potential losses that partially or completely offset gains, and illiquidity. Derivatives can create investment leverage. Gains or losses from derivatives can be substantially greater than the derivatives’ original cost and can sometimes be unlimited. If the value of a derivative does not correlate well with the particular market or asset class the derivative is designed to provide exposure to, the derivative may not have the effect anticipated. Derivatives can also reduce the opportunity for gains or result in losses by offsetting positive returns in other investments. Many derivatives are traded in the over-the-counter market and not on exchanges.

Dollar Roll and Reverse Repurchase Agreement Transaction RiskThese transactions generally create leverage and subject the Fund to the credit risk of the counterparty.

Fixed Income Securities RiskThe values of fixed income securities typically will decline during periods of rising interest rates, and can also decline in response to changes in the financial condition of the issuer, borrower, counterparty, or underlying collateral assets, or changes in market, economic, industry, political, and regulatory conditions affecting a particular type of security or issuer or fixed income securities generally. Certain events, such as market or economic developments, regulatory or government actions, natural disasters, terrorist attacks, war, and other geopolitical events can have a dramatic adverse effect on the debt market and the overall liquidity of the market for fixed income securities. During those periods, the Fund may experience high levels of shareholder

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redemptions, and may have to sell securities at times when the Fund would otherwise not do so, and potentially at unfavorable prices. Certain securities may be difficult to value during such periods. Fixed income securities are subject to interest rate risk (the risk that the value of a fixed income security will fall when interest rates rise), extension risk (the risk that the average life of a security will be extended through a slowing of principal payments), prepayment risk (the risk that a security will be prepaid and the Fund will be required to reinvest at a less favorable rate), and credit risk. These risks may be heightened due to the current historically low interest rate environment.

Foreign Investment Risk; Emerging Markets Risk; Currency RiskInvestments in securities of non-U.S. issuers (including depositary receipts) entail risks not typically associated with investing in securities of U.S. issuers. Similar risks may apply to securities traded on a U.S. securities exchange that are issued by

companies with significant exposure to non-U.S. countries. In certain countries, legal remedies available to investors may be more limited than those available with regard to U.S. investments. Because non-U.S. securities are normally denominated and traded in currencies other than the U.S. dollar, the value of the Fund’s assets may be affected favorably or

unfavorably by currency exchange rates, exchange control regulations, and restrictions or prohibitions on the repatriation of non-U.S. currencies. Income and gains with respect to investments in certain countries may be subject to withholding and other taxes. There may be less information publicly available about a non-U.S. company than about a U.S. company, and many non-U.S. companies are not subject to

accounting, auditing, and financial reporting standards, regulatory framework and practices comparable to those in the U.S. The securities of some non-U.S. companies, especially those in emerging markets, are less liquid and at times more volatile than securities of comparable U.S. companies. Emerging markets securities are subject to greater risks than securities issued in developed foreign markets, including less liquidity, greater price volatility, higher relative rates of inflation, greater political, economic, and social instability, greater custody and operational risks, and greater volatility in currency exchange rates. Non-U.S. transaction costs, such as brokerage commissions and custody costs may be higher than in the United States. In addition, there may be a possibility of

nationalization or expropriation of assets, imposition of currency exchange controls, confiscatory taxation,

political or financial instability, and diplomatic developments that could adversely affect the values of the Fund’s investments in certain non-U.S. countries.

Frequent Trading/Portfolio Turnover RiskPortfolio turnover generally involves some expense to the Fund and may result in the realization of taxable capital gains (including short-term gains). The trading costs and tax effects associated with portfolio turnover may adversely affect the Fund’s performance.

Inflation RiskThe value of assets or income from the Fund’s investments will be less in the future as inflation decreases the value of money. As inflation increases, the value of the Fund’s assets can decline as can the value of the Fund’s distributions.

Leveraging RiskInstruments and transactions, including derivatives and reverse repurchase

agreement transactions, that create leverage may cause the value of an investment in the Fund to be more volatile and all other risks will tend to be compounded.

Liquidity RiskCertain securities may be difficult (or impossible) to sell or positions difficult to close out at a desirable time and price, and the Fund may be required to hold an illiquid investment that is declining in value, or it may be required to sell certain illiquid investments at a price or time that is not advantageous in order to meet redemptions or other cash needs. Some securities may be subject to restrictions on resale.

Management RiskThe Fund relies on the manager’s investment analysis and its selection of investments to achieve its investment objective. There can be no assurance that the Fund will achieve the intended results and the Fund may incur significant losses.

Market RiskThe value of the Fund’s portfolio securities may decline, at times sharply and

unpredictably, as a result of unfavorable market-induced changes affecting particular industries, sectors, or issuers. Stock markets can decline significantly in response to issuer, market, economic, industry, political, regulatory, geopolitical and other conditions, as well as investor perceptions of these conditions. The Fund is subject to risks affecting issuers, such as management performance, financial leverage, industry problems, and reduced demand for goods or services.

Mortgage- and Asset-Backed Securities Risk

Investments in mortgage- and asset-backed securities subject the Fund to credit risk, interest rate risk,

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extension risk, and prepayment risk, among other risks. Mortgage-backed and asset-backed securities not issued by a government agency generally involve greater credit risk than securities issued by

government agencies. Payment of principal and interest generally depends on the cash flows generated by the underlying assets and the terms of the security. The types of mortgages (for example, residential or commercial mortgages) underlying securities held by the Fund may differ and be affected differently by market factors. Investments that receive only the interest portion or the principal portion of payments on the underlying assets may be highly volatile. The market for mortgage- and asset-backed securities has recently experienced high volatility and a lack of liquidity. As a result, the value of many of these securities has significantly declined.

Repurchase Agreement RiskThese transactions must be fully collateralized at all times, but involve some risk to a Fund if the other party should default on its obligation and the Fund is delayed or prevented from recovering the collateral.

Short Sales RiskIf the Fund sells a security short, it will make money if the security’s price goes down (in an amount greater than any transaction costs) and will lose money if the security’s price goes up. There is no limit on the amount of money the Fund may lose on a short sale. The Fund may not be able to close out a short sale when it might wish to do so, or may only do so at an unfavorable price. Short sales can involve leverage. If the Fund invests the proceeds from short positions in other securities the Fund could lose money both on the short positions and on the securities in which it has invested the short proceeds.

Sovereign Debt Obligations RiskInvestments in debt securities issued by governments or by government agencies and instrumentalities involve the risk that the governmental entities responsible for repayment may be unable or unwilling to pay interest and repay principal when due. Many sovereign debt obligations may be rated below investment grade (“junk” or “high yield” bonds). Any restructuring of a sovereign debt obligation held by the Fund will likely have a significant adverse effect on the value of the obligation. In the event of default of sovereign debt, the Fund may be unable to pursue legal action against the sovereign issuer or to realize on collateral securing the debt.

U.S. Government Securities RiskObligations of certain U.S. Government agencies and instrumentalities are not

backed by the full faith and credit of the U.S. Government, and there can be no assurance that the U.S. Government would provide financial support to such agencies and instrumentalities.

Valuation RiskThe Fund is subject to the risk of mispricing or improper valuation of its investments, in particular to the extent that its securities are fair valued.

When-Issued, Delayed Delivery, TBA, and Forward Commitment Transaction RiskThese transactions may create leverage and involve a risk of loss if the value of the securities declines prior to settlement. Performance Information

The following bar chart and table provide some indication of the risks of investing in the Fund. The bar chart shows changes in the Fund’s performance from year to year for Class I shares. The table shows how the Fund’s average annual returns for 1 year, and since inception, compare with those of a broad measure of market performance. The Fund’s name and investment strategy changed on October 27, 2014. The performance results shown below would not necessarily have been achieved had the Fund’s current investment strategy been in effect for the entire period for which performance results are presented. Performance for Class A shares of the Fund for periods prior to its inception date (04/01/14) is based on the performance of Class R5 shares, adjusted for Class A expenses. Performance for Class A shares of the Fund reflects any applicable sales charge. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. More up-to-date performance information is available at

http://www.massmutual.com/funds or by calling 1-888-309-3539. Annual Performance Class I Shares 2014 -2% 0% -4% 2% 4% 12% 10% 8% 6% 9.74% -1.43% 2013 2012 2005 2006 2007 2008 2009 2010 2011

N/A N/A N/A N/A N/A N/A

4.39% 2.41% Highest Quarter: 3Q ’12, 3.36% Lowest Quarter: 2Q ’13, ⳮ3.30%

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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 are not relevant to investors who hold Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. After-tax returns are shown for Class I only. After-tax returns for other classes will vary.

Average Annual Total Returns (for the periods ended December 31, 2014)

One Year

Since Inception (07/06/10)

Class I Return Before Taxes 4.39% 4.00% Return After Taxes on

Distributions 2.65% 2.68% Return After Taxes on

Distributions and Sales of

Fund Shares 2.74% 2.63% Class R5 Return Before Taxes 4.26% 3.82% Service

Class

Return Before Taxes

4.23% 3.74%

Admini-strative Class

Return Before Taxes

4.14% 3.63% Class A Return Before Taxes ⳮ1.06% 2.40% Class R4 Return Before Taxes 3.88% 3.52% Class R3 Return Before Taxes 3.66% 3.26% Barclays U.S. Aggregate Bond

Index (reflects no deduction for fees,

expenses, or taxes) 5.97% 3.78% MANAGEMENT

Investment Adviser:MML Investment Advisers, LLC

Subadviser:Metropolitan West Asset Management, LLC

Tad Rivelleis the Chief Investment Officer and a Generalist Portfolio Manager at MetWest. He has managed the Fund since October 2014.

Laird R. Landmannis the President and a Generalist Portfolio Manager at MetWest. He has managed the Fund since October 2014.

Stephen M. Kane, CFAis a Group Managing Director and Generalist Portfolio Manager at MetWest. He has managed the Fund since October 2014.

Bryan T. Whalen, CFAis a Group Managing Director and Generalist Portfolio Manager at MetWest. He has managed the Fund since October 2014.

PURCHASE AND SALE OF FUND SHARES Shares of the Fund are generally available to retirement plans, other institutional investors, and individual retirement accounts. Fund shares are redeemable on any business day by written request, telephone or internet (available to certain customers). TAX INFORMATION

The Fund intends to make distributions that may be taxed as ordinary income or capital gains, unless you are an investor eligible for preferential tax treatment. PAYMENTS TO BROKER-DEALERS AND OTHER FINANCIAL INTERMEDIARIES If you purchase the Fund through a broker-dealer or other financial intermediary, the intermediary may receive a one-time or continuing payments from the Fund, MML Advisers or its affiliates, or others for the sale of Fund shares or continuing shareholder services provided by the intermediary. These payments may create a conflict of interest by

influencing the broker-dealer or other intermediary to recommend the Fund over another investment. You should contact your intermediary to obtain more information about the compensation it may receive in connection with your investment.

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MassMutual Select Strategic Bond Fund

INVESTMENT OBJECTIVE

This Fund seeks a superior total rate of return by investing in fixed income instruments.

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. For Class A shares, you may qualify for sales charge discounts if you invest, or agree to invest in the future, at least $25,000 in MassMutual funds. More information about these and other discounts is available in the section titledSales Charges by Class

beginning on page 137 of the Fund’s Prospectus or from your financial professional.

Shareholder Fees(fees paid directly from your investment) Class I Class R5 Service Class Adminis-trative Class Class A Class R4 Class R3 Maximum Sales Charge (Load) Imposed on Purchases (as a % of offering

price) None None None None 4.75% None None

Maximum Deferred Sales Charge (Load) (as a % of the lower of the original offering price or redemption

proceeds) None None None None None None None

Annual Fund Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) Class I Class R5 Service Class Adminis-trative Class Class A Class R4 Class R3 Management Fees(1) _{.45% .45%} _.45% _.45% _{.45% .45% .45%} Distribution and Service (Rule 12b-1)

Fees None None None None .25% .25% .50% Other Expenses(1)_{.19% .29%} _.39% _.49% _{.49% .39% .39%} Total Annual Fund Operating Expenses .64% .74% .84% .94% 1.19% 1.09% 1.34% Expense Reimburse-ment (.16%) (.16%) (.16%) (.16%) (.16%) (.16%) (.16%) Total Annual Fund Operating Expenses after Expense Reimburse-ment(2) _{.48% .58%} _.68% _.78% _{1.03% .93% 1.18%}

(1) Management Fees and Other Expenses have been restated to reflect current fees.

(2) The expenses in the above table reflect a written agreement by MML Advisers to cap the fees and expenses of the Fund (other than extraordinary litigation and legal expenses, Acquired Fund fees and expenses, interest expense, short sale dividend and loan expense, or other non-recurring or unusual expenses such as organizational expenses and shareholder meeting expenses) through March 31, 2016, to the extent that Total Annual Fund Operating Expenses after Expense

Reimbursement would otherwise exceed .48%, .58%, .68%, .78%, 1.03%, .93%, and 1.18% for Classes I, R5, Service, Administrative, A, R4, and R3, respectively. The Total Annual Fund Operating Expenses after Expense Reimbursement shown in the above table may exceed these amounts, because, as noted in the previous sentence, certain fees and expenses are excluded from the cap. The agreement can only be terminated by mutual consent of the Board of Trustees on behalf of the Fund and MML Advisers.

Example

1 Year 3 Years 5 Years 10 Years

Class I $ 49 $189 $ 341 $ 783 Class R5 $ 59 $220 $ 396 $ 903 Service Class $ 69 $252 $ 450 $1,022 Administrative Class $ 80 $284 $ 504 $1,140 Class A $575 $820 $1,084 $1,836 Class R4 $ 95 $331 $ 585 $1,314 Class R3 $120 $409 $ 719 $1,599 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 308% of the average value of its portfolio. INVESTMENTS, RISKS, AND PERFORMANCE Principal Investment Strategies

Under normal circumstances, the Fund invests at least 80% of its net assets in U.S. dollar-denominated fixed income securities and other debt instruments of

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domestic and foreign entities, including corporate bonds, securities issued or guaranteed as to principal or interest by the U.S. Government or its agencies or instrumentalities, mortgage-backed or asset-backed securities, and money market instruments. The Fund may invest up to 20% of its total assets in non-U.S. dollar-denominated securities of these entities. The Fund may also invest in emerging markets. The Fund may but will not necessarily engage in foreign currency transactions, including forward contracts, options on currency, futures contracts, and swap contracts, to attempt to protect against adverse changes in currency exchange rates. In pursuing its investment objective, the Fund may (but is not obligated to) use a wide variety of additional exchange-traded and over-the-counter derivatives, including futures contracts (for hedging purposes or to adjust various portfolio characteristics, including the duration (interest rate volatility) of the Fund’s portfolio); interest rate swaps (for hedging purposes or to adjust various portfolio characteristics, including the duration (interest rate volatility) of the Fund’s portfolio); credit default swaps (for hedging purposes, to earn additional income, or as a substitute for direct investments); and hybrid instruments (as a substitute for direct investments). The Fund may also purchase and sell exchange-traded and over-the-counter options for hedging purposes, to adjust various portfolio characteristics, including the duration (interest rate volatility) of the Fund’s portfolio, or as a substitute for direct investments. Use of derivatives by the Fund may create investment leverage. The Fund may also invest in money market securities, including commercial paper. The Fund may hold a portion of its assets in cash or cash equivalents.

The Fund invests primarily in investment grade securities (rated Baa or higher by Moody’s or BBB or higher by Standard & Poor’s, or, if unrated,

determined by the subadviser to be of comparable quality), but may invest up to 25% of the portfolio in below investment grade debt securities (“junk” or “high yield” bonds), including securities in default. In the event that a security is downgraded after its purchase by the Fund, the Fund may continue to hold the security if the Fund’s subadviser,Western Asset Management Company(“Western Asset”), considers that doing so would be consistent with the Fund’s investment objective. The Fund may invest in domestic and foreign issuer loans and loan participations that pay interest at rates that float or reset periodically at a margin above a generally recognized base lending rate. Certain fixed income

securities in which the Fund may invest pay interest at variable or floating rates. Variable rate securities tend to reset at specified intervals, while floating rate securities may reset upon a change in a specified index rate. In most cases, these reset provisions reduce the impact of changes in market interest rates on the value of the security. However, some securities do not track the underlying index directly, but reset based on formulas that may produce a leveraging effect; others may also provide for interest payments that vary inversely with market rates. The market prices of these securities may fluctuate significantly when interest rates change. The Fund may invest in loans of companies whose financial condition is troubled or uncertain and that may be involved in bankruptcy proceedings, reorganizations, or financial restructurings. The Fund may also acquire, and subsequently hold, warrants and other equity interests. The Fund’s effective duration is normally expected to be between three and seven years. If the Fund’s effective duration falls outside of this range, the Fund will take action to bring it within its expected range within a reasonable period of time. Duration measures the price sensitivity of a bond to changes in interest rates. Duration is the dollar weighted average time to maturity of a bond utilizing the present value of all future cash flows. Effective duration measures the price sensitivity of a bond with embedded options to changes in interest rates. It provides a more accurate measure of price volatility when, due to the embedded options, the cash flow characteristics of the bond change as interest rates shift.

Western Asset invests in the fixed income markets seeking to exceed returns of the Fund’s benchmark while approximating benchmark risk. Western Asset focuses on sector allocation, issue selection, duration weighting, and term structure when buying and selling securities for the Fund. Western Asset emphasizes diversification, the use of multiple strategies and identification of long-term trends. The three key factors that determine the allocation decisions for the Fund are: Western Asset’s broad economic outlook, its review of historical yield spreads for debt instruments versus Treasuries, and its evaluation of changes in credit quality and the corresponding impact on prices. Western Asset will determine the portion of the Fund’s assets to be allocated to non-U.S. dollar denominated securities from time to time.Western Asset Management Company Limited(“Western Asset Limited”), an affiliate of Western Asset, has subadvisory responsibility for Western Asset’s non-U.S. dollar denominated investments. Western Asset Limited

MassMutual Select Funds

MassMutual

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Prospectus Inside

MASSMUTUAL SELECT FUNDS

Table Of Contents

MassMutual Select Total Return Bond Fund

MassMutual Select Strategic Bond Fund