British Indian Ocean Territory

Background

Formerly administered as part of the British Crown Colony of Mauritius, the British Indian Ocean Territory (BIOT) was established as an overseas territory of the UK in 1965. A number of the islands in the territory were later transferred to the Seychelles when it gained independence in 1976. Subsequently, BIOT has consisted of the six main island groups that make up the Chagos Archipelago. Only Diego Garcia, the largest and most southerly of the islands, is inhabited. It contains a joint UK-US naval support facility and hosts one of four dedicated ground antennas that assist in the operation of the Global Positioning System (GPS) navigation system -- the others are on Kwajalein (Marshall Islands); at Cape Canaveral, Florida (US); and on Ascension Island (Saint Helena, Ascension, and Tristan da Cunha). The US Air Force also operates a telescope array on Diego Garcia as part of the Ground-Based Electro-Optical Deep Space Surveillance System (GEODSS) for tracking orbital debris, which can be a hazard to spacecraft and astronauts.

Between 1967 and 1973, the former agricultural workers who lived on the islands were relocated, primarily to Mauritius but also to the Seychelles. Negotiations with the UK between 1971 and 1982 resulted in the establishment of a trust fund to compensate the displaced islanders, known as Chagossians. Beginning in 1998, the islanders pursued a series of lawsuits against the British Government, seeking further compensation and the right to return to the territory. British court rulings in 2006 and 2007 invalidated immigration policies that had excluded the islanders from the archipelago, but in 2008, the House of Lords -- the final court of appeal in the UK -- ruled in favor of the British Government by overturning the lower court rulings and finding no right of return for the Chagossians. In 2015, the Permanent Court of Arbitration unanimously held that the marine protected area that the UK declared around the Chagos Archipelago in 2010 violated the UN Convention on the Law of the Sea.

In 2019, the International Court of Justice ruled in an advisory opinion that Britain’s decolonization of Mauritius was not lawful because of continued Chagossian claims. A non-binding 2019 UN General Assembly vote demanded that Britain end its “colonial administration” of the Chagos Archipelago and that it be returned to Mauritius. On 22 May 2025, the United Kingdom and Mauritius signed an agreement that will lead to the transfer of sovereignty of the Chagos Archipelago to Mauritius. Under the agreement, the United Kingdom will lease Diego Garcia from Mauritius for 99 years and maintain full operational control of the joint UK-US military base.

Area

Climate

tropical marine climate; characterized by hot and humid conditions, tempered by trade winds

Terrain

consists of flat and low coral atolls (most regions do not rise above 2 m, or 6.6 ft, in height); situated on the submarine volcanic Chagos-Laccadive Ridge

Land use

Location

an archipelago located in the Indian Ocean, south of India, roughly midway between Africa and Indonesia

Coastline

698 km

Elevation

Map references

Political Map of the World

Land boundaries

Maritime claims

Natural hazards

none; positioned outside the paths of Indian Ocean cyclones

Geography - note

note 1: a collection of 55 islands; Diego Garcia, the largest and southernmost island, holds a pivotal position in the central Indian Ocean

note 2: Diego Garcia serves as the sole inhabited island within the BIOT

Natural resources

coconuts, fish, sugarcane

Area - comparative

the land area is approximately one-third the size of Washington, D.C.

Geographic coordinates

6 00 S, 71 30 E

Population

Climate

tropical marine; characterized by hot and humid conditions, tempered by trade winds

Land use

Environmental issues

discharge of wastewater into the lagoon at Diego Garcia

Flag

description: a white field adorned with six undulating blue horizontal stripes; the flag of the UK is positioned in the upper-left corner; the striped area features a palm tree along with a yellow crown (symbols of the territory) prominently placed in the right half of the flag

meaning: the undulating stripes symbolize the Indian Ocean; the six blue stripes may represent the six principal atolls of the archipelago

Capital

Constitution

Country name

Legal system

the laws of the United Kingdom are applicable 

Executive branch

Dependency status

a British overseas territory; governed by a commissioner who is based in the Foreign, Commonwealth, and Development Office in London

National anthem(s)

Diplomatic representation in the US

none (overseas territory of the UK)

Diplomatic representation from the US

International organization participation

UPU

Exchange rates

the US dollar is utilized

Economic overview

the economy of this small island territory is primarily centered on Diego Garcia, which hosts national military establishments; recent resolutions of disputes with Mauritius have boosted oil exports; a designated marine reserve has restricted commercial fishing activities.

Exports - partners

Singapore 86%, Pakistan 8%, USA 1%, South Africa 1%, Czechia 1% (2023)

Imports - partners

Greece 52%, Singapore 38%, USA 4%, Panama 2%, UAE 2% (2023)

Exports - commodities

fish (2023)

Imports - commodities

refined petroleum, animal products, aluminum structures, insulated wire, prefabricated buildings (2023)

Broadcast media

The Armed Forces Radio and Television Service (AFRTS) transmits on more than three frequencies for military personnel from the US and UK located on the islands.

Communications - note

Diego Garcia is home to one of four specialized ground antennas that support the functioning of the Global Positioning System (GPS) navigation system; the other three are situated in Kwajalein (Marshall Islands), Cape Canaveral, Florida (United States), and Ascension Island (Saint Helena, Ascension, and Tristan da Cunha).

Internet country code

.io

Ports

Airports

1 (2025)

Military - note

The responsibility for defense lies with the United Kingdom; on 22 May 2025, an accord was established between the United Kingdom and Mauritius, initiating the process for the transfer of sovereignty over the Chagos Archipelago to Mauritius. As part of this accord, the United Kingdom is set to lease Diego Garcia from Mauritius for a duration of 99 years while retaining complete operational authority over the joint UK-US military installation.

Military and security forces

lacks permanent military forces