Guantánamo Bay (Spanish: Bahía de Guantánamo) is a bay located in Guantánamo Province at the southeastern end of Cuba (19°54′N 75°9′W / 19.9°N 75.15°W / 19.9; -75.15). It is the largest harbor on the south side of the island and is surrounded by steep hills creating an enclave cut off from its immediate hinterland. In Britain in the 18th Century it was known as Cumberland Bay.

The United States assumed territorial control over Guantánamo Bay under the 1903 Cuban-American Treaty, which granted the United States a perpetual lease of the area. The current Cuban government considers the U.S. presence in Guantánamo to be illegal and the Cuban-American Treaty to have been procured by the threat of force in violation of international law.

The bay is located in Cuba and was originally named Guantánamo by the Taíno. Christopher Columbus landed at the location known as Fisherman's Point in 1494 naming it Puerto Grande. On landing, Columbus's crew found Taíno fishermen preparing a feast for the local chieftain. When Spanish settlers took control of the island, the bay became a vital harbor on the south side of the island.