Summary Prospectus Thornburg International Growth Fund

      FEBRUARY 1, 2016   CLASS R3: TIGVX  |  CLASS R4: TINVX  |  CLASS R5: TINFX  |  CLASS R6: THGIX        

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, 2016, are incorporated by reference into this Summary Prospectus.

 Investment Goal

The Fund seeks long-term growth of capital by investing in equity securities selected for their growth potential. 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 (fees paid directly from your investment)									(1)   Thornburg Investment Management, Inc. (“Thornburg”) and/or Thornburg Securities Corporation (“TSC”) have contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class R3, Class R4, Class R5 and Class R6 expenses do not exceed 1.50%, 1.40%, 0.99%, and 0.89%, 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, 2017, 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.
	Class R3		Class R4		Class R5		Class R6
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)		none		none		none		none
Maximum Deferred Sales Charge (Load) (as a percentage of redemption proceeds or original purchase price, whichever is lower)		none		none		none		none
Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
	Class R3		Class R4		Class R5		Class R6
Management Fees		0.82%		0.82%		0.82%		0.82%
Distribution and Service (12b-1) Fees		0.50%		0.25%		0.00%		0.00%
Other Expenses		0.66%		0.58%		0.38%		0.61%
Total Annual Fund Operating Expenses		1.98%		1.65%		1.20%		1.43%
Fee Waiver/Expense Reimbursement(1)		(0.48)%		(0.25)%		(0.21)%		(0.54)%
Total Annual Fund Operating Expenses After Fee Waiver/Expense Reimbursement		1.50%		1.40%		0.99%		0.89%

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 R3 Shares	$153	$575	$1,023	$2,268
Class R4 Shares	$143	$496	$873	$1,934

	1 Year	3 Years	5 Years	10 Years
Class R5 Shares	$101	$360	$639	$1,436
Class R6 Shares	$91	$399	$730	$1,667

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 92.01% of the average value of its portfolio.

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

Principal Investment Strategies

The Fund expects to invest primarily in equity securities from issuers around the world (primarily common stocks) selected for their growth potential and, under normal market conditions, invests at least 75% of its assets in foreign securities or depository receipts of foreign securities. However, the Fund may own a variety of securities, including domestic equity securities and partnership interests. The Fund may invest in developing countries.

The Fund’s investment advisor, Thornburg Investment Management, Inc. (“Thornburg”) intends to invest in companies that it believes will have growing revenues and earnings. The Fund can invest in companies of any size, from larger, well-established companies to smaller, emerging growth companies.

Thornburg primarily uses individual issuer and industry analysis to make investment decisions. Among the specific factors considered by Thornburg in identifying securities for inclusion in the Fund are:

•   earnings growth potential   •   business model   •   industry growth potential   •   industry leadership   •   asset appreciation potential   •   potential size of business   •   price/earnings ratio •   price/revenue ratio   •   PE/growth rate ratio   •   price/cash flow ratio   •   enterprise value/EBITDA (earnings before interest, taxes, depreciation and amortization) ratio   •   management strength   •   debt/capital ratio

The Fund typically makes equity investments in the following three types of companies:

Growth Industry Leaders: Companies in this category often have leadership positions in growing markets. In some cases these companies may have dominant market share. These companies tend to be larger and more established.

Consistent Growers: Companies in this category generally exhibit steady earnings or revenue growth, or both. These companies often have subscription or other recurring revenue profiles. Given their business models, these companies may outperform in weak markets.

Emerging Growth Companies: Companies often addressing a new market or carving out a niche in an existing market. Companies in this category may experience rapid growth, and tend to be smaller, earlier stage companies. Thornburg expects that companies in this category should generate high returns over time, but with higher volatility.

In conjunction with individual issuer analysis, Thornburg may identify economic sectors it expects to experience growth. At times this approach may produce a focus on certain industries, such as technology, financial services, healthcare or biotechnology. The exposure to particular economic sectors or industries likely will vary over time. Investment decisions are also based on domestic and international economic developments, outlooks for securities markets, interest rates and inflation, and the supply and demand for debt and equity securities.

Debt obligations, usually with associated equity features, occasionally will be considered for investment when Thornburg

believes them to be more attractive than equity alternatives. The Fund may purchase debt obligations of any maturity and of any credit quality, including “high yield” or “junk” bonds. There is no minimum credit quality or rating of debt obligation the Fund may purchase.

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.

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 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 protection.

Developing Country Risk – The risks which may affect investments in foreign issuers (see “Foreign Investment Risk,” above) 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 its business in developing countries.

Small and Mid-Cap Company Risk – Investments in small-capitalization companies and mid-capitalization companies may involve additional risks, which may be relatively higher with smaller companies. These additional risks may result from limited

2      Thornburg International Growth Fund • February 1, 2016 For the Fund’s Prospectus or SAI, visit www.thornburg.com/download

product lines, more 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 these 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 debt obligations may decline and the Fund’s share value and any dividends paid by the Fund may be reduced. 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 its 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 below beginning on page 38.

Past Performance of the Fund

The following information provides some indication of the risks of investing in International Growth 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 R3 shares vary in each full year shown. The average annual total return figures compare Class R3, Class R4, Class R5 and Class R6 share performance to the Morgan Stanley Capital International (MSCI) All Country (AC) World ex-U.S. Growth Index, a market capitalization weighted index which includes growth companies in developed and emerging markets throughout the world, excluding the United States. 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, 2015. 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 R3 Shares

Highest quarterly results for time period shown: 28.18%

(quarter ended 6-30-09).

Lowest quarterly results for time period shown: -12.87%

(quarter ended 9-30-11)

Average Annual Total Returns (periods ended 12-31-15)

Class R3 Shares	1 Year	5 Years	Since   Inception   (2-1-08)
Return Before Taxes	6.25%	8.38%	5.49%
Return After Taxes on Distributions	6.25%	7.93%	5.06%
Return After Taxes on Distributions and Sale of Fund Shares	3.54%	6.56%	4.23%
MSCI AC World ex-U.S. Growth Index (reflects no deduction for fees, expenses, or taxes)	-1.26%	2.13%	0.57%
Class R4 Shares	1 Year	5 Years	Since   Inception   (2-1-08)
Return Before Taxes	6.42%	8.53%	5.59%
MSCI AC World ex-U.S. Growth Index (reflects no deduction for fees, expenses, or taxes)	-1.26%	2.13%	0.57%
Class R5 Shares	1 Year	5 Years	Since   Inception   (2-1-08)
Return Before Taxes	6.82%	8.94%	6.02%
MSCI AC World ex-U.S. Growth Index (reflects no deduction for fees, expenses, or taxes)	-1.26%	2.13%	0.57%
Class R6 Shares	1 Year		Since   Inception   (2-1-13)
Return Before Taxes	6.91%		7.20%
MSCI AC World ex-U.S. Growth Index (reflects no deduction for fees, expenses, or taxes)	-1.26%		2.14%

After-tax returns are calculated using the highest historical 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 International Growth Fund • February 1, 2016 For the Fund’s Prospectus or SAI, visit www.thornburg.com/download       3

Management

Investment Advisor: Thornburg Investment Management, Inc.

Portfolio Managers:

Tim Cunningham, CFA, a managing director of Thornburg, has been one of the persons jointly and primarily responsible for management of the Fund since 2012.

Greg Dunn, a managing director of Thornburg, has been one of the persons jointly and primarily responsible for management of the Fund since 2012.

Purchase and Sale of Fund Shares

Eligible employer-sponsored retirement plans wishing to make Class R3, Class R4, 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 R3, Class R4, 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 R3, Class R4, 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 R3, Class R4, 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 this 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 the 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.

Click here to view the Fund’s Prospectus or SAI.

TH2257

4      Thornburg International Growth Fund • February 1, 2016 For the Fund’s Prospectus or SAI, visit www.thornburg.com/download