Mutual Fund Summary Prospectus (497k)

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Thornburg Developing World

Fund

February 1, 2014

Class R5: THDRX Class R6: TDWRX

Click here to view the Fund’s Prospectus or Statement of Additional Information.

Before you invest, you may want to review the Fund’s Prospectus and Statement of Additional Information (SAI), which contain more information about the Fund and its risks. You can find the Fund’s Prospectus, SAI and other information about the Fund online at www.thornburg.com/download. You can also get this information at no cost by calling 800.847.0200 or by sending an e-mail request to info@thornburg.com. The current Prospectus and SAI, dated February 1, 2014, are incorporated by reference into this Summary Prospectus.


Investment Goal The Fund’s primary investment goal is long-term capital appreciation. 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.

Shareholder Fees						(1) For the most recent fiscal year, the Fund had nominal Class R5 assets, and the actual expense ratio for that class (17.45%) bears no relation to the expected ratio when the classes has an expected level of assets. Therefore, other expenses are estimated for the current period. (2) Thornburg Investment Management, Inc. (“Thornburg”) and/or Thornburg Securities Corporation have contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class R5 and Class R6 expenses do not exceed 1.09% and 0.99%, respectively. The agreement to waive fees and reimburse expenses may be terminated by the Fund at any time, but may not be terminated by Thornburg or TSC before February 1, 2015, unless Thornburg or TSC ceases to be the investment advisor or distributor of the Fund prior to that date. Thornburg and TSC retain the ability to be repaid by the Fund for fee waivers and expense reimbursements during a fiscal year if Fund expenses fall below the relevant percentage threshold before the end of that fiscal year.
(fees paid directly from your investment)
	Class R5			Class R6
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)		none			none
Maximum Deferred Sales Charge (Load) (as a percentage of redemption proceeds or original purchase price, whichever is lower)		none			none
Annual Fund Operating Expenses
(expenses that you pay each year as a percentage of the value of your investment)
	Class R5			Class R6
Management Fees		0.82%			0.82%
Distribution and Service (12b-1) Fees		0.00%			0.00%
Other Expenses		0.73%	⁽¹⁾		1.17%

Total Annual Fund Operating Expenses		1.55%			1.99%
Fee Waiver/Expense Reimbursement ⁽²⁾		(0.46)%			(1.00)%

Total Annual Fund Operating Expenses After Fee Waiver/Expense Reimbursement		1.09%			0.99%

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, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions (and giving effect to fee waivers and expense reimbursements in the first year), your costs would be:


	1 Year	3 Years	5 Years	10 Years
Class R5 Shares	$111	$444	$801	$1,806
Class R6 Shares	$101	$528	$980	$2,236

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 61.67% of the average value of its portfolio.

Principal Investment Strategies

Under normal market conditions the Fund invests at least 80% of its assets in equity securities and debt obligations of developing country issuers. A developing country issuer is a company or sovereign entity that is domiciled or otherwise tied economically to one or more developing countries. The Fund expects that investments in the Fund’s portfolio normally will be weighted in favor of equity securities. The Fund’s investment in debt obligations may include, but is not limited to, those of sovereign and corporate issuers. The Fund may purchase debt obligations of any maturity and credit quality. There is no minimum credit quality or rating of debt obligation the Fund may purchase. The Fund also may invest in debt obligations which have a combination of equity and debt characteristics (such as convertible bonds). The Fund may invest in issuers of any size of capitalization, including small companies.

Currently, the Fund’s investment advisor, Thornburg Investment Management, Inc. (“Thornburg”) considers developing countries to include most Central and South American, African, Asian and Eastern European nations, including, but not limited to, Argentina, Austria, Brazil, Chile, China, Colombia, Czech Republic, Egypt, Hong Kong, Hungary, India, Indonesia, Israel, South Korea, Malaysia, Mexico, Morocco, Nigeria, Pakistan, Peru, Philippines, Poland, Qatar, Romania, the Russian Federation, Slovenia, South Africa, Taiwan, Thailand, Turkey, Ukraine, the United Arab Emirates and Vietnam. Thornburg identifies what it considers to be developing countries based upon its own analysis of measures of industrialization, economic growth, population growth and other factors, and may also consider classifications by the World Bank, the International Finance Corporation, the United Nations and independent financial services firms that maintain indices of developing countries.

Thornburg considers a variety of factors to determine whether an investment is tied economically to one or more developing countries, including (i) whether or not a significant portion of the

issuer’s revenues or assets are derived from or are located in developing countries, (ii) the primary trading market of the issuer’s securities, (iii) the locations of its offices or other operations, (iv) the source of any governmental guarantees or other supports, (v) identification of the issuer’s securities within an index or other listing indicating its location in a particular developing country or region, and (vi) whether the investment is otherwise exposed to the economic fortunes and risks of developing countries.

The Fund’s policy of investing at least 80% of its assets in developing country issuers may be changed by the Fund’s Trustees without a shareholder vote upon 60 days’ notice to shareholders.

Among the specific factors considered in identifying securities for inclusion in the Fund are domestic and international economic developments, outlooks for securities markets, interest rates and inflation, the supply and demand for debt and equity securities, and analysis of specific issuers. With respect to equity securities, the Fund typically makes investments in the following three types of issuers:

Basic Value: Companies which, in Thornburg’s opinion, are financially sound with well established businesses selling at low valuations relative to the companies’ net assets or potential earning power.

Consistent Earner: Companies which normally exhibit steady earnings growth, cash flow characteristics and/or dividend growth. These companies may have above average profitability measures and normally sell at above average valuations.

Emerging Franchise: Companies which, in Thornburg’s opinion, are in the process of establishing a leading position in a product, service or market with the potential to grow at an above average rate.

Principal Investment Risks

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares varies from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. The value of a security may change in response to developments affecting entire economies, markets or industries, including changes in interest rates, political and legal developments, and general market volatility. These risks may be more pronounced for the Fund’s investments in developing countries.

Risks Affecting Specific Issuers – The value of an equity security or debt obligation may decline in response to developments affecting the specific issuer of the security or obligation, even if the overall industry or economy is unaffected. These developments may


2		Thornburg Developing World Fund — February 1, 2014		For the Fund’s Prospectus or SAI , visit www.thornburg.com/download

include a variety of factors, including but not limited to management issues or other corporate disruption, a decline in revenues or profitability, an increase in costs, or an adverse effect on the issuer’s competitive position.

Foreign Investment Risk – Investments in securities of foreign issuers may involve risks including adverse fluctuations in currency exchange rates, political instability, confiscations, taxes or restrictions on currency exchange, difficulty in selling foreign investments, and reduced legal protections. These risks may be more pronounced for investments in developing countries because the economies of those countries are usually less diversified, communications, transportation and economic infrastructures are less developed, and developing countries ordinarily have less established legal, political, business and social frameworks. At times the prices of equity securities or debt obligations of a developing country issuer may be extremely volatile. An issuer domiciled in a developed country may be similarly affected by these developing country risks to the extent that the issuer conducts a significant percentage of its business in developing countries.

Smaller Company Risk – Investments in smaller companies may involve additional risks because of limited product lines, limited access to markets and financial resources, greater vulnerability to competition and changes in markets, lack of management depth, increased volatility in share price, and possible difficulties in valuing or selling the investments.

Credit Risk – If debt obligations held by the Fund are downgraded by ratings agencies or go into default, or if management action, legislation or other government action reduces the ability of issuers to pay principal and interest when due, the value of those obligations may decline and the Fund’s share value and any dividends paid by the Fund may be reduced. Some foreign government debt obligations may be subject to default, repudiation or renegotiation, delays in payment, or could be downgraded by ratings agencies. Additionally, because the ability of an issuer of a lower-rated or unrated debt obligation (including particularly “junk” or “high yield” bonds) to pay principal and interest when due is typically less certain than for an issuer of a higher-rated debt obligation, lower-rated and unrated debt obligations are generally more vulnerable than higher-rated debt obligations to default, to ratings downgrades, and to liquidity risk.

Interest Rate Risk – When interest rates increase, the value of the Fund’s investments in debt obligations may decline and the Fund’s share value may be reduced. This effect is typically more pronounced for intermediate and longer-term debt obligations. Decreases in market interest rates may result in prepayments of debt obligations the Fund acquires, requiring the Fund to reinvest at lower interest rates.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell some or all of the investments promptly, or may only be able to sell investments at less than desired prices. This risk may be more pronounced for the Fund’s investments in developing countries.

Additional information about Fund investments, investment strategies and risks of investing in the Fund appears beginning on page 38 of the Prospectus.

Past Performance of the Fund

The following information provides some indication of the risks of investing in Developing World Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class C shares have been different in each full year shown. The average annual total return figures compare Class C share performance to the Morgan Stanley Capital International (MSCI) Emerging Markets Index, which represents a broad measure of equity market performance of emerging markets. The returns reflected in the bar chart and in the table are for a class of shares that is not offered in this Prospectus but which would have substantially similar annual returns because the shares represent investments in the same portfolio of securities. Annual returns would differ only to the extent Class C shares are subject to a deferred sales charge on redemptions within 12 months of purchase and higher annual expenses before and after fee waivers and expense reimbursements than Class R5 or Class R6 shares. Class R5 and Class R6 shares were first offered to investors on February 1, 2013, and Class C shares were first offered to investors on December 16, 2009. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown below is as of the calendar year ended December 31, 2013. Updated performance information may be obtained on the Thornburg website at www.thornburg.com or by calling 1-800-847-0200.

Annual Total Returns – Class C Shares*

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Highest quarterly results for time period shown:

17.22% (quarter ended 3-31-12).

Lowest quarterly results for time period shown:

-23.36% (quarter ended 9-30-11).

The deferred sales which is imposed on redemptions of Class C shares within 12 months of purchase is not reflected in the returns in the bar chart, and the returns would be less if the charge was taken into account.

Average Annual Total Returns (periods ended

12-31-13)


Class C Shares	1 Year*			Since Inception 12-16-09*
Return Before Taxes		13.70	%		11.11	%

Return After Taxes on Distributions		13.70	%		11.11	%

Return After Taxes on Distributions and Sale of Fund Shares		7.75	%		8.76	%

MSCI Emerging Markets Index (reflects no deduction for fees, expenses, or taxes)		-2.60	%		3.20	%

*	Because Class R5 and Class R6 shares were not available before February 1, 2013, the returns shown are for Class C shares.

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


Thornburg Developing World Fund — February 1, 2014		For the Fund’s Prospectus or SAI , visit www.thornburg.com/download		3

Management

Investment Advisor: Thornburg Investment Management, Inc.

Portfolio Manager: Lewis Kaufman, CFA, a managing director of Thornburg, has been the portfolio manager of Developing World Fund since its inception.

For important information about the purchase and sale of Fund shares, the taxation of distributions by the Fund, and financial intermediary compensation, please turn to “Summary of Other Important Information Respecting Fund Shares” on page 37 of the Prospectus.

Purchase and Sale of Fund Shares

Eligible employer-sponsored retirement plans wishing to make Class R5 or Class R6 shares available to plan participants should contact a financial intermediary authorized to sell shares of the Funds. As a participant in an employer-sponsored retirement plan which makes Class R5 or Class R6 shares available, you may add shares to your account by contacting your plan administrator. Although the Funds do not currently impose any investment minimums on the purchase of Class R5 or Class R6 shares, your employer-sponsored retirement plan may establish such minimums. Contact your plan administrator for more information.

Please contact your retirement plan administrator if you wish to sell your Class R5 or Class R6 shares. Your plan administrator will conduct the transaction for you, or provide you with the means to conduct the transaction yourself.

Tax Information

Fund distributions to qualified retirement plan accounts, and transactions in Fund shares by those accounts, are not generally subject to current federal income tax under existing federal law. Please see “Taxes” on page 50 of the Prospectus for additional information. Purchasers are cautioned to seek the advice of their own advisors about the tax consequences of contributions to plan accounts and distributions from plan accounts.

Payments to Broker-Dealers and Other Financial Intermediaries

If you purchase shares of a Fund through a broker-dealer or other financial intermediary (such as a bank), the Fund, its investment advisor and/or its distributor may pay the intermediary for the sale of Fund shares and related services. These payments may create a conflict of interest by influencing the broker-dealer or other intermediary and your salesperson to recommend the Fund over another investment. Ask your salesperson or visit your financial intermediary’s website for more information.