The Chagos Archipelago is a group of seven atolls comprising more than 60 islands in the Indian Ocean about 500 kilometres south of the Maldives archipelago. This chain of islands is the southernmost archipelago of the Chagos–Laccadive Ridge, a long submarine mountain range in the Indian Ocean. In its north are the Salomon Islands, Nelson's Island and Peros Banhos; towards its south-west are the Three Brothers, Eagle, Egmont and Danger Island southeast of these is Diego Garcia, by far, the largest island. All are low-lying, save for a few extremely small instances, set around lagoons,
The Chagos, together with the Maldives and Lakshadweep, forms the Maldives-Lakshadweep-Chagos Archipelago tropical moist forests terrestrial ecoregion. The islands and their surrounding waters are a vast oceanic Environment Preservation and Protection Zone, an area twice the size of the UK's land surface.
The deep oceanic waters around the Chagos Islands, out to the 200 nautical mile limit, include an exceptional diversity of undersea geological features, These areas almost certainly harbour many undiscovered and specially adapted species. Although the deepwater habitats surrounding the islands have not been explored or mapped in any detail, work elsewhere in the world has shown that high physical diversity of the sea floor is closely linked to a high diversity of species.
The biodiversity of the Chagos archipelago and its surrounding waters is one of the main reasons it is so special. As of 2010, 76 species that call Chagos home were listed on the IUCN Red List of Threatened Species.