Capital and largest city of Puerto Rico, located on the northern coast of the island on the Atlantic Ocean. A major port and tourist resort of the West Indies, it is the oldest city now under U.S. jurisdiction. Originally the settlement was known as Puerto Rico and the island as San Juan, but over the centuries common usage brought about a reversalof the names.

In the 20th century San Juan expanded rapidly beyond its walled confines, now known as Old San Juan, to incorporate suburban Miramar, Santurce, and Condado, along the coast, as well as industrial Hato Rey, with its large sports stadium and modern financial district, and the town of Rio Piedras, immediately to the southeast. By 1980 the San Juan metropolitan area included the surrounding municipalities to the east and west and had about one-third of Puerto Rico's total population. In a move to decentralize the old city, many government offices and agencies were moved across the bay, but the governor's palace remains in use.

San Juan's international airport, just outside Old San Juan, is the busiest terminal in the Caribbean, and the area's resort hotels are among the largest and most luxurious in Latin America. In contrast to this prosperity is the historic squalor of San Juan's shanty towns and squatter villages.