Strategy. The Fund pursues its primary goal by investing principally in a laddered maturity portfolio of municipal obligations issued by states and state agencies, local governments and their agencies, and by United States territories and possessions. Thornburg Investment Management, Inc. (Thornburg) actively manages the Funds portfolio. Investment decisions are based upon outlooks for interest rates and securities markets, the supply of municipal debt obligations, and analysis of specific securities. The Fund invests primarily in obligations and participations in obligations which are rated by a nationally recognized statistical rating organization at the time of purchase as investment grade or, if unrated, are issued by obligors which Thornburg determines have comparable investment grade obligations outstanding or which are deemed by Thornburg to be … Show more… The Fund pursues its primary goal by investing principally in a laddered maturity portfolio of municipal obligations issued by states and state agencies, local governments and their agencies, and by United States territories and possessions. Thornburg Investment Management, Inc. (Thornburg) actively manages the Funds portfolio. Investment decisions are based upon outlooks for interest rates and securities markets, the supply of municipal debt obligations, and analysis of specific securities. The Fund invests primarily in obligations and participations in obligations which are rated by a nationally recognized statistical rating organization at the time of purchase as investment grade or, if unrated, are issued by obligors which Thornburg determines have comparable investment grade obligations outstanding or which are deemed by Thornburg to be comparable to obligors with outstanding investment grade obligations. The Fund may invest up to 20 percent of its net assets, plus the amount of any borrowings for investment purposes, in lower-quality municipal debt obligations rated by a nationally recognized statistical rating organization at the time of purchase as below investment grade (sometimes called junk bonds or high yield bonds) or, if unrated, issued by obligors which Thornburg determines have comparable below investment grade municipal obligations outstanding or which are deemed by Thornburg to be comparable to obligors with outstanding below investment grade obligations. Participations are undivided interests in pools of securities where the underlying credit support passes through to the participants. The Funds portfolio is laddered by investing in obligations of different maturities so that some obligations mature during each of the coming years. The Fund seeks to maintain a portfolio of investments having a dollar-weighted average effective duration of normally three to ten years. Duration is a measure of estimated sensitivity to interest rate changes. A portfolio with a longer average effective duration will typically be more sensitive to interest rate changes than a portfolio with a shorter average effective duration. Duration is commonly expressed as a number, which is the expected percentage change in an obligations price upon a 1% change in interest rates. For example, an obligation with a duration of 10 would be expected to change in price by approximately 10% in response to a 1% change in interest rates. During temporary periods the Funds average effective duration may be reduced for defensive purposes. There is no limitation on the duration or maturity of any specific security the Fund may purchase. The Fund may dispose of any security before it matures. The Fund also attempts to reduce changes in its share value through credit analysis, selection and diversification. 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 sell an investment prior to its scheduled maturity date to enhance income or reduce loss, to change the portfolios average duration, to pursue other investment opportunities, in response to changes in the conditions or business of the investments issuer or changes in overall market conditions, or if, in Thornburgs opinion, the investment no longer serves to achieve the Funds investment goals. The objective of preserving capital may prevent the Fund from obtaining the highest yields available. The Fund normally invests at least 80% of its net assets, plus the amount of any borrowings for investment purposes, in municipal obligations the income from which is exempt from the regular federal income tax, though the income on those investments may still be subject to the federal alternative minimum tax (AMT). Gains realized on investments held by the Fund and not offset by realized losses will be subject to federal income tax. Show less