American Beacon S&P 500 Index Fund

American Beacon S&P 500^® Index Fund

Investment Objective

The Fund's investment objective is to replicate as closely as possible, before expenses, the performance of the Standard & Poor's 500 Index (“S&P 500 Index” or “Index”).

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.

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

Annual Fund Operating Expenses American Beacon S&P 500 Index Fund		Institutional Class	Investor Class
Management fees	[1]	0.045%	0.045%
Distribution and/or service (12b-1) fees	[1]	none	none
Other expenses	[1]	0.095%	0.555%
Total annual fund operating expenses	[1]	0.14%	0.60%

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 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:

Expense Example American Beacon S&P 500 Index Fund (USD $)	1 year	3 years	5 years	10 years
Institutional Class	14	45	79	179
Investor Class	61	192	335	750

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. The Fund invests substantially all of its investable assets in the State Street Equity 500 Index Portfolio, a series of State Street Master Funds; therefore, the Fund's portfolio turnover rate is that of the State Street Equity 500 Index Portfolio. During the most recent fiscal year, the Fund's portfolio turnover rate was 4% of the average value of its portfolio.

Principal Investment Strategies

The Fund seeks to achieve its investment objective by investing substantially all of its investable assets in the State Street Equity 500 Index Portfolio (the “Portfolio”), a series of State Street Master Funds (the “Master Funds”), which has the same investment objective as, and investment policies that are substantially similar to those of the Fund. The discussion below refers to investments made by the Portfolio. For easier reading, in this Prospectus, the term “Fund” includes the Portfolio.

The Portfolio uses a passive management strategy designed to track the performance of the S&P 500 Index. The Index is a well-known stock market index that includes common stocks of 500 companies from a number of sectors representing a significant portion of the market value of all stocks publicly traded in the United States.

The Portfolio is not managed according to traditional methods of “active” investment management, which involve the buying and selling of securities based upon economic, financial and market analysis and investment judgment. Instead, the Portfolio, using a “passive” or “indexing” investment approach, attempts to replicate as closely as possible, before expenses, the performance of the S&P 500 Index.

The Portfolio generally intends to invest in all 500 stocks comprising the S&P 500 Index in approximate proportion to their weightings in the Index. However, under various circumstances, it may not be possible or practicable to purchase all 500 stocks in those weightings. In those circumstances, the Portfolio may purchase a sample of the stocks in the Index in proportions expected by the Portfolio's investment adviser, SSgA Funds Management, Inc. (the “Adviser” or “SSgA FM”), to match generally the performance of the Index as a whole. In addition, from time to time stocks are added to or removed from the Index. The Portfolio may sell securities that are represented in the Index, or purchase securities that are not yet represented in the Index, in anticipation of their removal from or addition to the Index. Under normal market conditions the Portfolio will not invest less than 80% of its total assets in stocks in the Index.

The Portfolio may at times purchase or sell futures contracts on the Index, or options on those futures, in lieu of investing directly in the stocks making up the Index. The Portfolio might do so, for example, in order to increase its investment exposure pending investment of cash in the stocks comprising the Index. Alternatively, the Portfolio might use futures or options on futures to reduce its investment exposure in situations where it intends to sell a portion of the stocks in its portfolio but the sale has not yet been completed. The Portfolio may also enter into other derivative transactions, including the use of options or swap transactions, to assist in attempting to replicate the performance of the Index. The Portfolio may also, to the extent permitted by applicable law, invest in shares of other mutual funds whose investment objectives and policies are similar to those of the Portfolio.

Principal Risks

There is no assurance that the Fund will achieve its investment objective and you could lose part or all of your investment in the Fund. The Fund is not designed for investors who need an assured level of income and is intended to be a long-term investment. The Fund is not a complete investment program and may not be appropriate for all investors. Investors should carefully consider their own investment goals and risk tolerance before investing in the Fund.

The discussion below refers to the principal risks associated with an investment in the Portfolio. Because the Fund invests substantially all of its assets in the Portfolio, the principal risks associated with an investment in the Portfolio are the same as those associated with an investment in the Fund. The principal risks of investing in the Portfolio are:

Stock Market Risk

Stock values could decline generally or could under-perform other investments.

Large Capitalization Companies Risk

Because the S&P 500 includes mainly large U.S. companies, the Portfolio's emphasis on securities issued by large capitalization companies makes it susceptible to the risks of investing in larger companies. For example, larger companies may be unable to respond as quickly as smaller companies to competitive challenges. Larger companies also tend not to be able to maintain the high growth rates of well-managed smaller companies, especially during strong economic periods.

Index Tracking Risk

The Portfolio's return may not match the return of the Index for a number of reasons. For example, the return on the securities and other investments selected by the Adviser may not correlate precisely with the return on the Index. The Portfolio incurs a number of operating expenses not applicable to the Index, and incurs costs in buying and selling securities. The Portfolio may not be fully invested at times, either as a result of cash flows into the Portfolio or reserves of cash held by the Portfolio to meet redemptions. The return on the sample of securities purchased by the Portfolio, or futures or other derivative positions taken by the Portfolio, to replicate the performance of the Index may not correlate precisely with the return of the Index.

Derivatives Risk

Derivative transactions typically involve leverage and may be highly volatile. It is possible that a derivative transaction will result in a loss greater than the principal amount invested, and the Portfolio may not be able to close out a derivative transaction at a favorable time or price.

Passive Strategy/Index Risk

The Portfolio is managed with a passive investment strategy, attempting to track the performance of an unmanaged index of securities. This differs from an actively managed fund, which typically seeks to outperform a benchmark index. As a result, the Portfolio may hold constituent securities of the Index regardless of the current or projected performance of a specific security or a particular industry or market sector. Maintaining investments in securities regardless of market conditions or the performance of individual securities could cause the Portfolio's return to be lower than if the Portfolio employed an active strategy.

Investment Risk

An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. When you sell your shares of the Fund, they could be worth less than what you paid for them. Therefore, you may lose money by investing in the Fund.

Master/Feeder Structure Risk

Unlike a traditional mutual fund that invests directly in securities, the Fund pursues its objective by investing substantially all of its assets in the Equity 500 Index Portfolio, which has substantially the same investment objectives, policies and restrictions. The ability of the Fund to meet its investment objective is directly related to the ability of the Portfolio to meet its objective. The ability of the Fund to meet its objective may be adversely affected by the purchase and redemption activities of other investors in the Portfolio. The ability of the Fund to meet redemption requests depends on its ability to redeem its interest in the Portfolio.

Fund Performance

The bar chart and table below provide an indication of risk by showing how the Fund's performance has varied from year to year. The table shows how the Fund's performance compares to a broad-based market index. The chart and the table below show the performance of the Fund's Investor Class shares for all periods. You may obtain updated performance information on the Fund's website at www.americanbeaconfunds.com. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.

Calendar year total returns for Investor Class shares

Highest Quarterly Return:	15.83%
(1/1/04 through 12/31/13)	(3rd Quarter 2009)
Lowest Quarterly Return:	-21.99%
(1/1/04 through 12/31/13)	(4th Quarter 2008)

Average Annual Total Returns For the periods ended December 31, 2013

Average Annual Returns American Beacon S&P 500 Index Fund		1 Year	5 Years	10 Years	Inception Date
Investor Class	[1]	31.56%	17.32%	6.81%	Mar. 02, 1998
Investor Class After Taxes on Distributions	[1]	30.75%	16.96%	6.53%	Mar. 02, 1998
Investor Class After Taxes on Distributions and Sales	[1]	17.82%	14.00%	5.49%	Mar. 02, 1998
Institutional Class	[1]	32.15%	17.85%	7.30%	Dec. 31, 1996
S&P 500 Index	[1]	32.39%	17.94%	7.41%

[1] The fees and expenses shown in the table and the example that follows include both the expenses of the Fund and the Fund's proportionate share of the allocated expenses of the State Street Equity 500 Index Portfolio, a series of State Street Master Funds.

[1] After-tax returns are shown only for Investor Class shares; after-tax returns for other share classes will vary. 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. If you hold your Fund shares through a tax-deferred arrangement, such as an IRA or a 401(k), the after-tax returns do not apply to your situation.