Strategy. The fund invests, under normal market conditions, at least 80% of its net assets in securities and other investments, the interest on which is exempt from federal income tax. Interest from the funds investments may be subject to the federal alternative minimum tax. MFS (Massachusetts Financial Services Company, the fund's investment adviser) normally invests the funds assets primarily in municipal instruments. MFS may invest 25% or more of the funds total assets in municipal instruments that finance similar types of projects, such as those relating to education, healthcare, housing, utilities, water, or sewers. MFS may invest up to 100% of the funds assets in below investment grade quality debt instruments. MFS may invest a significant percentage of the fund's assets … Show more… The fund invests, under normal market conditions, at least 80% of its net assets in securities and other investments, the interest on which is exempt from federal income tax. Interest from the funds investments may be subject to the federal alternative minimum tax. MFS (Massachusetts Financial Services Company, the fund's investment adviser) normally invests the funds assets primarily in municipal instruments. MFS may invest 25% or more of the funds total assets in municipal instruments that finance similar types of projects, such as those relating to education, healthcare, housing, utilities, water, or sewers. MFS may invest up to 100% of the funds assets in below investment grade quality debt instruments. MFS may invest a significant percentage of the fund's assets in issuers in a single state, territory, or possession, or a small number of states, territories, or possessions. While MFS may use derivatives for any investment purpose, to the extent MFS uses derivatives, MFS expects to use derivatives primarily to increase or decrease exposure to a particular market, segment of the market, or security, to increase or decrease interest rate exposure, or as alternatives to direct investments. Derivatives include futures, forward contracts, options, inverse floating rate instruments, and swaps. MFS uses an active bottom-up investment approach to buying and selling investments for the fund. Investments are selected primarily based on fundamental analysis of individual instruments and their issuers. Quantitative screening tools that systematically evaluate instruments may also be considered. In structuring the fund, MFS also considers top-down factors. For purposes of the fund's 80% policy, net assets include the amount of any borrowings for investment purposes. Show less