Puerto Rico is governed by the Constitution of the Commonwealth of Puerto Rico, approved by the U.S. Congress and ratified by the people in 1952. Puerto Ricans have been U.S. citizens since 1917 and can vote in presidential elections while living in the United States but not in Puerto Rico. Since 1980 they can participate locally in presidential primaries. Puerto Ricans do not pay federal income taxes.

Modeled after that of the United States, the government of Puerto Rico has three main branches - the executive, legislative, and judiciary. All elected officials - the governor, resident commissioner in the U.S. Congress (who has only committee voting privileges), senators, representatives, mayors, and members of the local assemblies - serve 4-year terms and stand for election on the same day as national elections are held in the United States. The legislature is bicameral, with a Senate and a House of Representatives. Local government is represented through the 78 municipios. Each municipio has an urban seat with the same name and a series of smaller units called barrios. A mayor and political assembly is elected every four years in each municipio. Barrios are the smallest political unit and were originally mostly rural in nature. Over time many have become urban barrios or wards. The judicial branch includes a supreme court with 7 judges as well as an intermediate appellate court, superior courts, and municipal courts. Under judicial reform, district judgeships are being phased out as sitting judges retire or die. Cases can be appealed to Puerto Rico's Supreme Court and eventually to the U.S. Supreme Court. Violations of U.S. federal laws are considered directly at the U.S. federal court level.

Traditionally, three major political parties have existed, each representing one of the three political alternatives with regard to association with the United States. The New Progressive party is a proponent of the U.S. statehood option, the Popular Democratic party supports a continued commonwealth status, and the Puerto Rican Independence party supports political independence. The first two are majority parties while the latter is a minority party. The Popular Democratic party has been in power for most of the years since 1940, although it was defeated in elections of the 1990s. With the 2000 elections, it again took power, winning the gubernatorial office and legislative majorities in Puerto Rico, as well as the lone seat of resident commissioner in the U.S. Congress.