A debt security issued by municipalities. The income from municipal bonds is usually exempt from federal income taxes. It may also be exempt from state income taxes in the state in which the municipal bond is issued. Some municipal bond interest could be subject to the federal alternative minimum tax. If you sell a municipal bond at a profit, you could incur capital gains taxes. The principal value of bonds fluctuates with market conditions. Bonds sold prior to maturity may be worth more or less than their original cost.