Strategy. Under normal market conditions, at least 80% of the income from the Fund will be exempt from federal income tax (the Tax-Exempt 80% Policy). In complying with this policy, the Fund normally expects to invest at least 80% of its net assets in municipal obligations, the interest on which is exempt from regular federal income tax and federal alternative minimum tax (the Municipal Obligations 80% Policy). The Fund normally invests at least 80% of its net assets (plus any borrowings for investment purposes) in issuers that the investment adviser determines operate in a manner consistent with or promote The Calvert Principles for Responsible Investment (the Principles) (the Principles 80% Policy). The Principles provide a framework for the investment advisers evaluation … Show more… Under normal market conditions, at least 80% of the income from the Fund will be exempt from federal income tax (the Tax-Exempt 80% Policy). In complying with this policy, the Fund normally expects to invest at least 80% of its net assets in municipal obligations, the interest on which is exempt from regular federal income tax and federal alternative minimum tax (the Municipal Obligations 80% Policy). The Fund normally invests at least 80% of its net assets (plus any borrowings for investment purposes) in issuers that the investment adviser determines operate in a manner consistent with or promote The Calvert Principles for Responsible Investment (the Principles) (the Principles 80% Policy). The Principles provide a framework for the investment advisers evaluation of investments considering environmental, social and governance (ESG) factors. The Principles seek to identify issuers that operate in a manner that is consistent with or promote: environmental sustainability and resource efficiency; equitable societies and respect for human rights; and accountable governance and transparency, among other factors. For additional information, please refer to Appendix A: The Calvert Principles for Responsible Investment in this Prospectus. At least 65% of the Funds net assets normally will be invested in municipal obligations rated at least investment grade at the time of investment (which are those rated Baa or higher by Moodys Investors Service, Inc. (Moodys), or BBB or higher by either S&P Global Ratings (S&P) or Fitch Ratings (Fitch)) or, if unrated, determined by the investment adviser to be of at least investment grade quality. The Fund may invest up 35% of its net assets in obligations rated below investment grade and in unrated obligations considered to be of comparable quality by the investment adviser (junk bonds). For purposes of rating restrictions, if municipal obligations are rated differently by two or more rating agencies, the highest rating is used. The Fund may invest in municipal obligations without limitation as to their maturity or duration, and there is no upper or lower limit on the Funds average maturity or average duration. At the sole discretion of the Funds portfolio managers, the Fund may seek out attractive investment opportunities across the yield curve. The Fund may invest in a variety of municipal obligations, including obligations issued by state and local issuers as well as U.S. territories, various types of revenue debt, special tax obligations, qualified private activity bonds, municipal leases, principal only municipal investments and certificates of participation in such investments. The Fund may invest 25% or more of its total assets in certain types of municipal obligations (such as general obligations, municipal leases, principal only municipal investments, revenue bonds and industrial development bonds) and in one or more economic sectors (such as housing, hospitals, healthcare facilities or utilities). The Fund may invest in pooled investment vehicles, including exchange-traded funds (ETFs), in order to seek exposure to the municipal markets or municipal market sectors. Such investments in pooled investment vehicles will not be counted toward the Principles 80% Policy or toward the Tax-Exempt 80% Policy but may be counted toward the Municipal Obligations 80% Policy if the vehicle invests at least 80% of its net assets in the type of securities included in the Municipal Obligations 80% Policy. The Fund may invest in restricted securities. The Fund may invest in other debt obligations, including (but not limited to) taxable municipal obligations, U.S. Treasury securities and obligations of the U.S. Government, its agencies and instrumentalities (Agency Securities) provided that not more than 20% of its income will be taxable. Interest earned from taxable investments will be taxed as ordinary income. Dividends attributable to interest on certain private activity bonds are included in federal alternative minimum tax for individuals. The Fund may purchase or sell futures contracts for hedging purposes. The Fund may also purchase or sell residual interest bonds. The Fund may also lend its securities. The investment advisers process for selecting obligations for purchase and sale includes an evaluation of an obligations creditworthiness and consideration of the responsible investing criteria described below. In evaluating creditworthiness, the investment adviser will consider ratings assigned by rating agencies and generally perform additional credit and investment analysis. The investment adviser will also consider the relative value of the obligation in the market. Responsible Investing. In selecting investments for the Fund, the Funds investment adviser is guided by the Principles (a copy of which is included as an appendix to the Funds Prospectus), which provide a framework for considering ESG factors. The Funds investments include municipal securities that the Funds adviser believes may have a positive environmental and/or social impact, such as obligations that fund education, healthcare, community services, housing, water, public transportation and other public purposes. Show less