Diego Garcia is an island of the British Indian Ocean Territory, a disputed overseas territory of the United Kingdom also claimed by Mauritius. It is a militarised atoll just south of the equator in the central Indian Ocean, and the largest of the 60 small islands of the Chagos Archipelago. Portuguese sailors under Pedro Mascarenhas were the first Europeans to discover the island, finding it uninhabited in 1512. After a 1786 British colony failed, the French began using the island as a leper colony and, starting in 1793, coconut cultivation by enslaved labor. It was transferred to British rule after the Napoleonic Wars. It was one of the "Dependencies" of the British Colony of Mauritius until the Chagos Islands were detached for inclusion in the newly created British Indian Ocean Territory (BIOT) in 1965.

The British Indian Ocean Territory (BIOT) is an Overseas Territory of the United Kingdom situated in the Indian Ocean, halfway between Tanzania and Indonesia. The territory comprises the seven atolls of the Chagos Archipelago with over 1,000 individual islands, many very small, amounting to a total land area of 60 square kilometres. The largest and most southerly island is Diego Garcia, 27 square kilometres, the site of a Joint Military Facility of the United Kingdom and the United States. Official administration is remote from London, though the local capital is often regarded as being on Diego Garcia.