San Juan is the capital and largest municipality in Puerto Rico. As of the 2000 census, it has a population of 433,733, making it the 42nd-largest city under the jurisdiction of the United States. San Juan was founded by Spanish colonists in 1521, who called it Ciudad de Puerto Rico ("Rich Port City"). Puerto Rico's capital is the second oldest European-established city in the Americas, after Santo Domingo, now in the Dominican Republic. Several historical buildings are located in San Juan; among the most notable are the city's former defensive forts, Fort San Felipe del Morro and Fort San Cristobál, and La Fortaleza, the oldest executive mansion in continuous use in the Americas.

Today, San Juan serves as one of Puerto Rico's most important seaports,[4] and is the island's manufacturing, financial, cultural, and tourism center. The population of the Metropolitan Statistical Area, including San Juan and the municipalities of Bayamón, Guaynabo, Cataño, Canóvanas, Caguas, Toa Alta, Toa Baja, Carolina and Trujillo Alto, is about 2 million inhabitants; thus, about half the population of Puerto Rico now lives and works in this area. San Juan is also a principal city of the San Juan-Caguas-Fajardo Combined Statistical Area. The city has been the host of numerous important events within the sports community, including the 1979 Pan American Games, 1966 Central American and Caribbean Games, 2006 World Baseball Classic and the Caribbean Series.

Originally, the city of San Juan was called Puerto Rico meaning "rich port", and the entire island was called San Juan. The capital and the island's names were later accidently switched.