What are municipal bonds?

Municipal bonds ("munis") are debt securities issued by states, cities, counties, school districts, and other governmental entities to finance public infrastructure projects such as roads, bridges, hospitals, schools, water systems, and airports. The US municipal bond market exceeds $4 trillion in outstanding debt and serves as the primary financing mechanism for American public infrastructure.

The defining feature of municipal bonds is their tax-exempt status. Interest income from most municipal bonds is exempt from federal income tax, and if the investor resides in the issuing state, the income may also be exempt from state and local taxes. This "triple tax exemption" makes munis particularly valuable for investors in high tax brackets. A municipal bond yielding 3.5% provides the same after-tax income as a taxable bond yielding approximately 5.5% for an investor in the 37% federal tax bracket.

Munis come in two primary forms. General obligation (GO) bonds are backed by the full taxing power of the issuing government and are considered lower risk because the government can raise taxes to service the debt. Revenue bonds are backed by the cash flows from a specific project (a toll road, airport, or water system) and carry higher risk because they depend on the project's financial performance. The risk profile varies enormously: bonds issued by well-managed states and large cities carry credit risk comparable to high-grade corporates, while bonds from distressed municipalities (Detroit, Puerto Rico, Harrisburg) have resulted in defaults and restructurings.

The municipal market has unique technical dynamics. Retail investors and mutual funds are the dominant holders, unlike the corporate bond market which is dominated by institutional investors. This retail orientation means that municipal prices can be influenced by tax-loss selling in December, seasonal demand patterns, and flows into and out of muni mutual funds. For portfolio construction, munis offer uncorrelated credit risk relative to corporate bonds and provide a steady, tax-efficient income stream that is difficult to replicate with other asset classes.