San Juan is the capital of, and at about 395,000, the largest city in, Puerto Rico. It has one of the best harbors in the Caribbean. The city celebrates its fifth century in 2008 or 2021, depending on whether one counts from the founding of the original settlement at Caparra or the act of moving the Caparra settlement to Puerto Rico isle (now Old San Juan).

Technological advances after World War II in the development of the airliner, coupled with the island's climate and natural setting, have transformed San Juan into the springboard for tourism around the island, and has made the rest of the Caribbean known throughout the world during the last fifty years. Today the capital features numerous hotels, museums, historical buildings, restaurants, beaches and shopping centers. In San Juan there are numerous tourist attractions, including: Old San Juan, Ocean Park, Isla Verde and Condado.

Places and monuments emphasized in tourism campaigns include: Old San Juan, promoting the historic nature of its colonial buildings and narrow streets covered by adoquine, a blue stone cast from furnace slag; they were brought over as ballast on Spanish ships. This includes the city's ancient defensive wall and forts, most notably El Morro and the Castle of San Cristóbal. On January 23, 1984 both of these edifices were catalogued as being part of humanity's cultural patrimony. The numerous restaurants and art galleries in the zone are frequently visited by tourists. The local universities are promoted as historic places, most notably the campus of University of Puerto Rico located in Río Piedras, which is the oldest university on the island being founded in 1903.