Summary Prospectus by Investment Company - Form 497K

BlackRock Funds III |Class G Shares

Class G: BSPGX

Before you invest, you may want to review the Fund's prospectus, which contains more information about the Fund and its risks. You can find the Fund's prospectus (including amendments and supplements), reports to shareholders and other information about the Fund, including the Fund's statement of additional information, online at https://www.blackrock.com/prospectus. You can also get this information at no cost by calling (800) 537-4942 or by sending an e-mail request to [email protected], or from your financial professional. The Fund's prospectus and statement of additional information, both dated April 29, 2024, as amended and supplemented from time to time, are incorporated by reference into (legally made a part of) this Summary Prospectus.

This Summary Prospectus contains information you should know before investing, including information about risks. Please read it before you invest and keep it for future reference.

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

Summary Prospectus

Key Facts About iShares S&P 500 Index Fund

Investment Objective

iShares S&P 500 Index Fund (the "Fund"), a series of BlackRock Funds III (the "Trust"), seeks to provide investment results that correspond to the total return performance of publicly-traded common stocks in the aggregate, as represented by the Standard & Poor's 500® Index (the "S&P 500 Index" or the "Underlying Index").

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy, hold and sell Class G Shares of the Fund. You may pay other fees, such as brokerage commissions and other fees to your financial professional or your selected securities dealer, broker, investment adviser, service provider or industry professional (including BlackRock Fund Advisors ("BFA") and its affiliates) (each, a "Financial Intermediary"), which are not reflected in the table and example below.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)		Class G Shares
Management Fee1,2		0.01%
Distribution and/or Service (12b-1) Fees		None
Other Expenses3,4		0.00%
Administration Fees4	0.00%
Independent Expenses3	-
Total Annual Fund Operating Expenses4		0.01%
Fee Waivers and/or Expense Reimbursements2,3		-
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements2,3,4		0.01%

Example:

This Example is intended to help you compare the cost of investing in shares of the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in shares of the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

	1 Year	3 Years	5 Years	10 Years
Class G Shares	$1	$4	$7	$16

Portfolio Turnover:

The Master Portfolio 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 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 Master Portfolio's portfolio turnover rate was 10% of the average value of its portfolio.

Principal Investment Strategies of the Fund

The Fund pursues its investment objective by seeking to replicate the total return performance of the S&P 500 Index, which is composed of approximately 500 selected common stocks, most of which are listed on the New York Stock Exchange (the "NYSE"). The S&P 500 Index is a capitalization-weighted index from a broad range of industries chosen for market size, liquidity and industry group representation. The component stocks are weighted according to the total float-adjusted market value of their outstanding shares (i.e., they are weighted according to the public float which is the total market value of their outstanding shares readily available to the general marketplace for trading purposes). The percentage of the Fund's assets invested in a given stock is approximately the same as the percentage such stock represents in the S&P 500 Index.

The Fund is managed by determining which securities are to be purchased or sold to reflect, to the extent feasible, the investment characteristics of its benchmark index. Under normal circumstances, at least 90% of the value of the Fund's assets, plus the amount of any borrowing for investment purposes, is invested in securities comprising the S&P 500 Index.

The Fund is a "feeder" fund that invests all of its assets in the Master Portfolio of MIP, which has the same investment objective and strategies as the Fund. All investments are made at the Master Portfolio level. This structure is sometimes called a "master/feeder" structure. The Fund's investment results will correspond directly to the investment results of the Master Portfolio. For simplicity, the prospectus uses the name of the Fund or the term "Fund" (as applicable) to include the Master Portfolio.

Principal Risks of Investing in the Fund

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. An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The following is a summary description of the principal risks of investing in the Fund. The relative significance of each risk factor below may change over time and you should review each risk factor carefully.

An index fund has operating and other expenses while an index does not. As a result, while the Fund will attempt to track the S&P 500 Index as closely as possible, it will tend to underperform the index to some degree over time. If an index fund is properly correlated to its stated index, the fund will perform poorly when the index performs poorly.

differences (including, as applicable, differences between a security's price at the local market close and the Fund's valuation of a security at the time of calculation of the Fund's net asset value), differences in transaction costs, the Fund's holding of uninvested cash, differences in timing of the accrual of or the valuation of dividends or other distributions, interest, the requirements to maintain pass-through tax treatment, portfolio transactions carried out to minimize the distribution of capital gains to shareholders, changes to the Underlying Index and the cost to the Fund of complying with various new or existing regulatory requirements, among other reasons. These risks may be heightened during times of increased market volatility or other unusual market conditions. In addition, tracking error may result because the Fund incurs fees and expenses, while the Underlying Index does not.

An outbreak of an infectious coronavirus (COVID-19) that was first detected in December 2019 developed into a global pandemic that has resulted in numerous disruptions in the market and has had significant economic impact leaving general concern and uncertainty. Although vaccines have been developed and approved for use by various governments, the duration of the pandemic and its effects cannot be predicted with certainty. The impact of this coronavirus, and other epidemics and pandemics that may arise in the future, could affect the economies of many nations, individual companies and the market in general ways that cannot necessarily be foreseen at the present time.

Performance Information

The information shows how the Fund's performance has varied year by year and provides some indication of the risks of investing in the Fund. Class G Shares commenced operations on July 1, 2019. As a result, the returns in the chart and the average annual total returns table for Class G Shares, prior to their commencement of operations on July 1, 2019, are based on the Fund's Class K Shares, which are offered in a separate prospectus. The average annual total return table compares the Fund's performance to that of the S&P 500 Index. To the extent that dividends and distributions have been paid by the Fund, the performance information of the Fund in the chart and table assumes reinvestment of the dividends and distributions. As with all such investments, past performance (before and after taxes) is not an indication of future results. The table includes all applicable fees. If BFA and its affiliates had not waived or reimbursed certain Fund expenses during these periods, the Fund's returns would have been lower. Updated information on the Fund's performance, including its current net asset value, can be obtained by visiting www.blackrock.com or can be obtained by phone at (800) 882-0052.

Class G Shares
ANNUAL TOTAL RETURNS
iShares S&P 500 Index Fund
As of 12/31

During the ten-year period shown in the bar chart, the highest return for a quarter was 20.52% (quarter ended June 30, 2020) and the lowest return for a quarter was -19.53% (quarter ended March 31, 2020).

For the periods ended 12/31/23 Average Annual Total Returns	1 Year	5 Years	10 Years
iShares S&P 500 Index Fund - Investor G Shares
Return Before Taxes	26.26 %	15.68 %	12.01 %
Return After Taxes on Distributions	25.76 %	15.11 %	11.43 %
Return After Taxes on Distributions and Sale of Fund Shares	15.84 %	12.53 %	9.82 %
S&P 500 Index (Reflects no deduction for fees, expenses or taxes)	26.29 %	15.69 %	12.03 %

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on the investor's tax situation and may differ from those shown, and the after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Investment Adviser

The Master Portfolio's investment adviser is BlackRock Fund Advisors (previously defined as "BFA").

Portfolio Managers

Portfolio Manager	Portfolio Manager of the Master Portfolio Since	Title
Paul Whitehead	2022	Managing Director of BlackRock, Inc.
Jennifer Hsui, CFA	2016	Managing Director of BlackRock, Inc.

Purchase and Sale of Fund Shares

Class G Shares are available only to investors on eligible platforms. Eligible platforms are those where clients invest in the Fund through a single omnibus account in the name of a Financial Intermediary that meets an initial investment minimum of $2 billion. For clients investing through such eligible platforms, the Fund does not impose investment minimums on any individual investor. Please contact your Financial Intermediary for information on any eligibility requirements.

Tax Information

Different income tax rules apply depending on whether you are invested through a qualified tax-exempt plan described in section 401(a) of the Internal Revenue Code of 1986, as amended. If you are invested through such a plan (and Fund shares are not "debt-financed property" to the plan), then the dividends paid by the Fund and the gain realized from a redemption or exchange of Fund shares will generally not be subject to U.S. federal income taxes until you withdraw or receive distributions from the plan. If you are not invested through such a plan, then the Fund's dividends and gain from a redemption or exchange may be subject to U.S. federal income taxes and may be taxed as ordinary income or capital gains, unless you are a tax-exempt investor.

Payments to Broker/Dealers and Other Financial Intermediaries

If you purchase shares of the Fund through a Financial Intermediary, the Fund and BlackRock Investments, LLC, the Fund's distributor, or its affiliates may pay the Financial Intermediary for the sale of Fund shares and related services. These payments may create a conflict of interest by influencing the Financial Intermediary and your individual financial professional to recommend the Fund over another investment.

Class G Shares are only available through a Financial Intermediary if the Financial Intermediary will not receive from Fund assets, or the Fund's distributor's or an affiliate's resources, any commission payments, shareholder servicing fees (including sub-transfer agent and networking fees), or distribution fees (including Rule 12b-1 fees) with respect to assets invested in Class G Shares.

Ask your individual financial professional or visit your Financial Intermediary's website for more information.