MASSMUTUAL SELECT T. ROWE PRICE RETIREMENT 2055 FUND CLASS M3 (MMDOX) Exchange: NMFQS

Principal Investment Strategies The Fund is a “fund of funds” and pursues its objective by investing in a diversified portfolio of other stock and bond series of both the MassMutual Select Funds and T. Rowe Price Funds that represent various asset classes and sectors (“Underlying Funds”). The Fund’s allocation between stock and bond funds will change over time in relation to its target retirement date. The Fund is subadvised by T. Rowe Price Associates, Inc. (“T. Rowe Price”). The Underlying Funds in which the Fund invests are predominantly either advised or subadvised by T. Rowe Price. The Fund is managed based on the specific retirement year (target date 2055) included in its name and assumes a retirement age of 65. The target date refers to the approximate year an investor in the Fund would plan to retire and likely stop making new investments in the Fund. The Fund is primarily designed for an investor who anticipates retiring at or about the target date and who plans to withdraw the value of the account in the Fund gradually after retirement. However, if an investor retires earlier or later than age 65, the Fund may not be an appropriate investment even if the investor retires on or near the Fund’s target date. Over time, the allocation to asset classes and funds will change according to a predetermined “glide path” shown in the following chart. The glide path represents the shifting of asset classes over time and shows how the Fund’s asset mix becomes more conservative–both prior to and after retirement–as time elapses. This reflects the need for reduced market risks as retirement approaches and the need for lower portfolio volatility after retiring. Although the glide path is meant to dampen the Fund’s potential volatility as retirement approaches, the Fund is not designed for a lump sum redemption at the retirement date. The Fund pursues an asset allocation strategy that promotes asset accumulation prior to retirement, but it is intended to also serve as a post-retirement investment vehicle with allocations designed to support an income stream made up of regular withdrawals throughout retirement along with some portfolio growth that exceeds inflation. After the target date, the Fund is designed to balance longevity and inflation risks along with the need for some income, although it does not guarantee a particular level of income. At the target date, the Fund’s allocation to stocks is anticipated to be approximately 55% of its assets. The Fund’s exposure to stocks will continue to decline until approximately 30 years after its target date, when its allocation to stocks will remain fixed at approximately 20% of its assets and the remainder will be invested in bonds. There are no maturity restrictions within the Fund’s overall allocation to bonds, although the bond funds in which the Fund invests may impose specific limits on maturity or credit quality. The allocations shown in the glide path are referred to as “neutral” allocations because they do not reflect any tactical decisions made by T. Rowe Price to overweight or underweight a particular asset class or sector based on its market outlook. The target allocations assigned to the broad asset classes (Stocks and Bonds), which reflect these tactical decisions resulting from market outlook, are not expected to vary from the neutral allocations set forth in the glide path by more than plus (+) or minus (-) five percentage (5%) points. The following table details the way the portfolio is generally expected to be allocated between the asset classes. The table also shows the expected allocations to the Underlying Funds that will be used within those asset classes. The information in the table represents the neutral allocations for the Fund as of February 1, 2020. The target allocations and actual allocations may differ. The Fund’s shareholder reports set forth its actual allocations between stock funds and bond funds and to the individual Underlying Funds. T. Rowe Price may modify the target asset allocation strategy or the selection of Underlying Funds from time to time, and may invest in other Underlying Funds, including any Underlying Funds that may be created in the future. At any given time, the Fund’s asset allocation may be affected by a variety of factors (such as, for example, whether an Underlying Fund is accepting additional investments). A description of the Underlying Funds is included in Appendix D of the Statement of Additional Information (“SAI”). Stock Funds 90.00 % MM S&P 500 Index 6.87 % MM Select T. Rowe Price Large Cap Blend 39.22 % MM Select T. Rowe Price Small and Mid Cap Blend 13.76 % MM Select T. Rowe Price International Equity 25.65 % MM Select T. Rowe Price Real Assets 4.50 % Bond Funds 10.00 % MM Select T. Rowe Price Bond Asset 6.00 % T. Rowe Price Dynamic Global Bond 1.00 % MM Select T. Rowe Price U.S. Treasury Long-Term 2.00 % T. Rowe Price Institutional High Yield 0.28 % T. Rowe Price High Yield 0.12 % T. Rowe Price Institutional Floating Rate 0.10 % MM Select T. Rowe Price Emerging Markets Bond 0.50 % MM Select T. Rowe Price Limited Duration Inflation Focused Bond 0.00 % Because the Fund will invest in Underlying Funds advised by MML Advisers, T. Rowe Price, or their affiliates, the Fund will not invest in funds advised or sponsored by others, even if they are less expensive or have better historical performance records. T. Rowe Price will be subject to a conflict of interest in selecting Underlying Funds, because its selection of Underlying Funds might appear to be influenced by the expected effect of the selection on its revenues or other benefits of the selection to it. T. Rowe Price has advised the Fund that, as a fiduciary to the Fund, T. Rowe Price has a duty to put the best interests of the Fund ahead of its own interest and that, consequently, it will make investment decisions for the Fund in the best interest of the Fund to achieve the Fund’s investment objectives and not for the benefit of T. Rowe Price. Through its investments in Underlying Funds, the Fund may be exposed to a wide range of securities and other instruments with differing characteristics (such as credit quality, duration, geography, industry, and market capitalization), including, but not limited to, equity securities of small-, mid-, or large-capitalization U.S. or non-U.S. issuers (including issuers that may only recently have become public companies), fixed income securities of U.S. or non-U.S. private or governmental issuers (including “junk” or “high yield” bonds, including securities in default), inflation-protected securities, bank loans, and short-term investments of any kind. Equity securities may include common stocks, preferred stocks, securities convertible into common or preferred stock, real estate investment trusts (“REITs”), rights, and warrants. An Underlying Fund may engage in foreign currency exchange transactions, including forward contracts, options on currency, futures contracts, and swap contracts, to take long or short positions in foreign currencies in order to enhance its investment return or to attempt to protect against adverse changes in currency exchange rates. An Underlying Fund may be permitted to use a wide variety of additional exchange-traded and over-the-counter derivatives, including options, futures contracts, swap contracts (including interest rate swaps, total return swaps, and credit default swaps), and hybrid instruments. An Underlying Fund may typically use these derivatives for hedging purposes, as a substitute for direct investments, to earn additional income, to gain exposure to securities or markets in which it might not be able to invest directly, or to adjust various portfolio characteristics, including the duration (interest rate volatility) of the Fund’s portfolio of debt securities. Use of derivatives by an Underlying Fund may create investment leverage. An Underlying Fund may enter into repurchase agreement transactions. An Underlying Fund may invest in mortgage-backed or other asset-backed securities. Some investments by an Underlying Fund may be restricted as to resale or otherwise considered to be illiquid. The Fund will bear a pro rata share of the Underlying Funds’ expenses. The Fund also bears all of the risks associated with the investment strategies used by the Underlying Funds.