Municipal bonds, or Muni bonds, are often referred to as tax-free municipal bonds. However, this isn’t always the case.
The United States Constitution prohibits different the levels of government from taxing each other. Thus, the Federal Government cannot levy taxes on State government, and vice versa. What that means is that all bonds issued by state or local governments, commonly known as Muni bonds, are exempt from Federal Income taxes. In order to be truly tax-free bonds, however, they must also be exempt from local income taxes as well. Most state governments exempt the interest payments from their own muni bonds from state taxes as a matter of convention. However, this exemption does not cross state lines. Thus, only municipal bonds held by residents of the states that issued them are fully tax-exempt.