Puerto Rico, a US territory since its invasion in 1898, is by far the most populous non-independent territory. It is the easternmost of the Greater Antilles chain in the Caribbean. The population density, highest around San Juan, is comparable with the Netherlands and is higher than in any US state. The tropical climate attracts growing numbers of tourists, 80% from the USA, and there have been major efforts to expand hotel and resort facilities.

Puerto Rico was granted its current commonwealth status in 1952, four years after an abortive pro-independence uprising. The inhabitants have US citizenship but only limited self-government. In three plebiscites, in 1967, 1993, and 1998, the islanders endorsed continued commonwealth status rather than opting for either US statehood or independence. The most recent of these votes was extremely close, but the pro-statehood governor who called the 1993 and 1998 votes, Pedro Rossello, was replaced by the anti-statehood Sila Calderón – the first female governor of Puerto Rico – in 2001.

Although thousands of the mostly Spanish-speaking Puerto Ricans have migrated to the US mainland in search of higher wages, the islanders have one of the highest living standards in the region. Tax relief, cheap labor, and the island's role as an export-processing zone, mainly for the US market, attracted many businesses. Clothing, electronics, petrochemical, and pharmaceutical industries traditionally dominated, but the decision to phase out tax exemptions for companies reinvesting in the island caused a slump in 1996, and more emphasis is now being placed on the service sector. New industries include health care and clinical testing, biotechnology, and other knowledge-based areas.

Governor Calderón spearheaded the campaign to stop the US navy from using the populated eastern island of Vieques for bombing practice. In 2000 an invasion of the bombing range by protestors led to some high-profile arrests, including that of Robert Kennedy Jr. A year later newly elected US president George W. Bush announced that the navy would not use the island after 2003.