Puerto Rico is a commonwealth: it has internal self-government, but the United States controls its foreign relations and defense, and operates the postal service and customs service. Residents of Puerto Rico are United States citizens, but do not pay federal income taxes or vote in presidential elections. They elect a delegate, called a resident commissioner to a four-year term, to the U.S. House of Representatives who can vote only in committees and when the House is sitting as a committee of the whole. Puerto Rico has the option to choose independence and end its association with the United States, or to seek statehood, but in repeated referendums it has voted to continue its commonwealth status.

Under the 1952 constitution there is separation of powers among the executive, legislative, and judicial branches. The governor, the chief executive officer of Puerto Rico, is elected by the people for four years and may be reelected indefinitely. He appoints other top executive officials.

The legislature, called the Legislative Assembly, consists of a senate of 29 members and a house of representatives of 53, all elected for four-year terms. It meets in regular session from January through May and during September and October. The governor has the power to call special sessions at any time. There are 8 senatorial districts and 42 representative districts in Puerto Rico. In each senatorial district, voters elect 2 senators, and in each representative district, voters elect 1 representative. They also elect 11 senators and 11 representatives ‘at-large’ — that is, from the entire commonwealth, rather than from districts.

The judiciary is headed by the Supreme Court of seven members appointed by the governor with the consent of the Senate. The retirement age of the justices is 70 years. There is a Circuit Court of Appeals which consists of 39 judges, each appointed by the governor to 16-year terms. The 210 superior court judges in Puerto Rico are appointed to 12-year terms and the 105 municipal judges are appointed to 8-year terms. The U.S. District Court for Puerto Rico, which has seven judges appointed by the U.S. president, hears cases involving federal law.

Puerto Rico is divided into 78 municipios, which, in turn, are divided into barrios, ciudades, pueblos, and subbarrios. There are no incorporated places. The places listed earlier in this article as "cities" are census designated places—closely settled population centers delineated by the U.S. Census Bureau and the Puerto Rican government. A mayor and an assembly are elected by the voters in each municipality. The mayor appoints a secretary-auditor and a treasurer.

The two dominant parties in Puerto Rico are the New Progressive Party, which wants Puerto Rico to become a U.S. state, and the Popular Democratic Party, which is in favor of continuing the island's commonwealth status. The Independence Party, a third party, favors independence for the island.