The Chagos Archipelago (Oil Islands) is a group of seven atolls comprising more than 60 individual tropical islands roughly in the centre of the Indian Ocean.

The Chagos lies about 500 km (300 miles) due south of the Maldives, its nearest neighbour, 1600 km (1000 miles) southwest of India, half way between Tanzania and Java. It's called Feyhandheebu by Maldivians and Phehandweep (Hindi: फेहंद्वीप) in North Indian languages and Paeikaana Theevukal (Tamil: பேகான தீவுகள்).

The Chagos group is a combination of different coralline structures topping a submarine ridge running southwards across the centre of the Indian Ocean, formed by volcanoes above the Réunion hotspot. Unlike in the Maldives there is not a clearly discernible pattern of arrayed atolls, which makes the whole archipelago look somewhat chaotic. Most of the coralline structures of the Chagos are submerged reefs.

Officially part of the British Indian Ocean Territory, the Chagos were home to the Chagossians for more than a century and a half until the United Kingdom and the United States expelled them in the 1960s in order to allow the US to build a military base on Diego Garcia, the largest of the Chagos Islands. The deal was sanctioned by the then British Secretary of State for Defence, Denis Healey.