Mutual Fund Summary Prospectus (497k)

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Thornburg Limited Term

Income Fund

February 1, 2014

Class A: THIFX Class C: THICX Class I: THIIX

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 primary goal of Income Fund is to provide as high a level of current income as is consistent, in the view of the Fund’s investment advisor, with safety of capital. As a secondary goal, the Fund seeks to reduce changes in its share prices compared to longer term portfolios.

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. You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds. More information about these and other discounts is available from your financial professional and in “Opening Your Account – Buying Fund Shares” on page 72 of the Prospectus.

Shareholder Fees

(1) A 0.50% contingent deferred sales charge (CDSC) is imposed on redemptions of any part or all of a purchase of $1 million or more within 12 months of purchase.

(2) Imposed only on redemptions of Class C shares within 12 months of purchase.

(fees paid directly from your investment)

Class A

Class C

Class I

Maximum Sales Charge (Load)

1.50%

none

Imposed on Purchases

(as a percentage of offering price)

Maximum Deferred Sales Charge

none

⁽¹⁾

0.50%

⁽²⁾

none

(Load) (as a percentage of redemption

proceeds or original purchase price, whichever is lower)

Annual Fund Operating Expenses

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

Class A

Class C

Class I

Management Fees

0.42%

Distribution and Service (12b-1) Fees

0.25%

0.50%

0.00%

Other Expenses

0.21%

0.20%

0.11%

Total Annual Fund Operating Expenses

0.88%

1.12%

0.53%

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, your costs would be:


	1 Year	3 Years	5 Years	10 Years
Class A Shares	$238	$426	$630	$1,218
Class C Shares	$164	$356	$617	$1,363
Class I Shares	$54	$170	$296	$665

You would pay the following expenses if you did not redeem your Class C shares:


	1 Year	3 Years	5 Years	10 Years
Class C Shares	$114	$356	$617	$1,363

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 36.66% of the average value of its portfolio.

Principal Investment Strategies

Thornburg Investment Management, Inc. (“Thornburg”) actively manages the Fund’s portfolio in pursuing the Fund’s investment goals. While Thornburg follows domestic and international economic developments, outlooks for securities markets, interest rates and inflation, the supply and demand for debt obligations, and other factors, the Fund’s investments are determined by individual security analysis. The Fund ordinarily acquires and holds securities for investment rather than for realization of gains by short-term trading on market fluctuations. However, it may dispose of any security prior to its scheduled maturity to enhance income or reduce loss, to change the portfolio’s average maturity, or to otherwise respond to current market conditions.

The Fund invests at least 65% of its net assets in (i) obligations of the U.S. government, its agencies and instrumentalities, and (ii) debt obligations rated at the time of purchase in one of the three highest ratings of Standard & Poor’s Corporation (AAA, AA or A) or Moody’s Investors Services, Inc. (Aaa, Aa or A) or, if no credit rating is available, judged to be of comparable quality by Thornburg. The Fund will not invest in any debt obligation rated at the time of purchase lower than BBB by Standard & Poor’s or Baa by Moody’s or of equivalent quality as determined by Thornburg. The Fund may purchase debt obligations such as corporate debt obligations, mortgage-backed securities, other asset-backed securities, municipal securities, and commercial paper and bankers’ acceptances. The Fund may purchase foreign securities of the same types and quality as the domestic securities it purchases when

Thornburg believes these investments are consistent with the Fund’s objectives.

Because the magnitude of changes in the value of interest-bearing obligations is greater for obligations with longer terms given an equivalent change in interest rates, the Fund seeks to reduce changes in its share value by maintaining a portfolio of investments with a dollar-weighted average maturity or expected life of normally less than five years. There is no limitation on the maturity of any specific security the Fund may purchase, and the Fund may sell any security before it matures. The Fund also attempts to reduce changes in share value through credit analysis, selection and diversification.

Principal Investment Risks

Although the Fund may acquire obligations issued or guaranteed by the U.S. government and its agencies, instrumentalities and enterprises, neither the Fund’s net asset value nor its dividends are guaranteed by the U.S. government. 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 government agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares and its dividends may fluctuate from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. If your sole objective is preservation of capital, then the Fund may not be suitable for you because the Fund’s share value will fluctuate, including as interest rates change. Investors whose sole objective is preservation of capital may wish to consider a high quality money market fund. 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.

Interest Rate Risk – When interest rates increase, the value of the Fund’s investments may decline and the Fund’s share value may be reduced. This effect is typically more pronounced for intermediate and longer-term obligations. This effect is also typically more pronounced for the Fund’s investment in mortgage- and other asset-backed securities, the value of which may fluctuate more significantly in response to interest rate changes. When interest rates decrease, the Fund’s dividends may decline.

Prepayment Risk – When market interest rates decline, certain debt obligations held by the Fund may be repaid more quickly than anticipated, requiring the Fund to reinvest the proceeds of those repayments in obligations which bear a lower interest rate. Conversely, when market interest rates increase, certain debt obligations held by the Fund may be repaid more slowly than anticipated, causing assets of the Fund to remain invested in relatively lower yielding obligations. These risks may be more pronounced for the Fund’s investments in mortgage-backed and asset-backed securities.

Credit Risk – All securities owned by the Fund may be subject to default, delays in payment, adverse legislation or other government action, or could be downgraded by ratings agencies, reducing the value of the Fund’s shares. Securities backed by the full faith and


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

credit of the U.S. government, such as U.S. Treasury obligations, are commonly regarded as having small exposure to credit risk. Obligations of certain U.S. government agencies, instrumentalities and government sponsored enterprises (sometimes referred to as “agency obligations”) are not direct obligations of the United States, may not be backed by the full faith and credit of the U.S. government, and may have a greater exposure to credit risk. Although the U.S. government is required by law to provide credit support for some agency obligations, there is no assurance that the U.S. government would provide financial support for any such obligation on a default by the issuing agency, instrumentality or enterprise in the absence of a legal requirement to do so. As of the date of this Prospectus, securities backed by the full faith and credit of the U.S. government, and securities of U.S. government agencies, instrumentalities and enterprises which may be purchased by the Fund, are rated “Aaa” by Moody’s Investors Services or “AA+” by Standard and Poor’s Corporation. Ratings agencies may reduce the ratings of any securities in the future. Lower-rated or unrated obligations held by the Fund may have, or may be perceived to have, greater risk of default and ratings downgrades.

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. For example, a fall in worldwide demand for U.S. government securities or general economic decline could lower the value of those securities.

Foreign Investment Risk – Investments in the debt obligations 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.

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 obligations promptly, or may only be able to sell obligations at less than desired prices.

Additional information about Fund investments, investment strategies, and risks of investing in the Fund appears on page 65 of the Prospectus.

Past Performance of the Fund

The following information provides some indication of the risks of investing in Income 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 A shares have been different in each full year shown. The average annual total return figures compare Class A, Class C and Class I share performance to the Barclays Intermediate Government/Credit Bond Index, a broad measure of market performance. 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 A Shares

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Highest quarterly results for time period shown: 6.76%

(quarter ended 6-30-09).

Lowest quarterly results for time period shown: -2.65%

(quarter ended 9-30-08).

The sales charge for Class A shares is not reflected in the returns shown in the bar chart above and the returns would be less if the charge was taken into account.

Average Annual Total Returns (periods ended 12-31-13)


Class A Shares	1 Year	5 Years	10 Years
Return Before Taxes	-1.67%	6.58%	4.21%

Return After Taxes on Distributions	-2.90%	5.15%	2.79%

Return After Taxes on Distributions and Sale of Fund Shares	-0.84%	4.63%	2.74%

Barclays Intermediate Govt/Credit Index (reflects no deduction for fees, expenses, or taxes)	-0.86%	3.96%	4.09%
Class C Shares	1 Year	5 Years	10 Years
Return Before Taxes	-0.82%	6.64%	4.12%

Barclays Intermediate Govt/Credit Index (reflects no deduction for fees, expenses, or taxes)	-0.86%	3.96%	4.09%
Class I Shares	1 Year	5 Years	10 Years
Return Before Taxes	0.26%	7.28%	4.73%

Barclays Intermediate Govt/Credit Index (reflects no deduction for fees, expenses, or taxes)	-0.86%	3.96%	4.09%

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. The after-tax returns shown relate only to Class A shares, and after-tax returns will vary for Class C and Class I shares because the returns of the classes are different.

Management

Investment Advisor: Thornburg Investment Management, Inc.

Co-Portfolio Managers:

Jason Brady, CFA, a managing director of Thornburg, has been one of the persons primarily responsible for management of the Fund since 2007.

Lon Erickson, CFA, a managing director of Thornburg, has been one of the persons primarily responsible for management of the Fund since 2010.


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

Purchase and Sale of Fund Shares

Minimum Initial Purchase

Class A and C Shares

$5,000 per Fund per account for individual investors.

$2,000 per Fund per account for individual retirement accounts.

$2,500 per Fund per account for financial intermediaries purchasing for accounts of others within a “wrap” asset allocation program, unless a different amount is specified by the wrap program’s provider.

Class I Shares

$2,500,000 per Fund per account for individual investors and qualified institutions (e.g., corporations, banks, insurance companies, trusts, endowments and foundations) purchasing for their own account.

$100,000 per Fund per account for financial intermediaries purchasing for accounts of others within a fee-based advisory program.

Minimum Subsequent Purchases

All Classes

$100 per Fund per account (unless purchasing through a financial intermediary that specifies a different minimum amount).

Redemptions

You can redeem some or all of your Fund shares at any time by mail (c/o the Fund’s Transfer Agent, Boston Financial Data Services, at P.O. Box 219017, Kansas City, Missouri 64121-9017), by telephone (1-800-847-0200), or through your financial intermediary.

Tax Information

Distributions to shareholders will generally be taxable to shareholders as ordinary income or capital gains for federal income tax purposes. Distributions may also be subject to state and local taxes. See “Taxes” on page 84 of the Prospectus.

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.