The Indian Ocean is the third largest ocean (73,427,000 sq km), extending from South Asia to Antarctica and from East Africa to South East Australia. It is 6,400 km wide at the equator. It constitutes about 20% of the world's total ocean area.

The Indian Ocean is connected with the Pacific Ocean by passages through the Malay Archipelago and between Australia and Antarctica; and with the Atlantic Ocean by the expanse between Africa and Antarctica and by the Suez Canal. Its chief arms are the Arabian Sea (with the Red Sea, the Gulf of Aden, and the Persian Gulf), the Bay of Bengal, and the Andaman Sea.

The continental shelf of the Indian Ocean is narrow. Madagascar and Sri Lanka, the largest islands in the ocean, are structurally parts of the continents as are Socotra, the Andaman Islands, and the Nicobar Islands; the Seychelles and the Kerguelen Islands are exposed tops of submerged ridges.

The Laccadives, the Maldives, and the Chagos are low coral islands, and Mauritius and Réunion are high volcanic cones. The floor of the Indian Ocean has an average depth of c.11,000 ft (3,400 m). The greatest depth (25,344 ft/7,725 m) is in the Java Trench, South of Java, Indonesia.

The Indian Ocean receives the waters of the Zambezi, Tigris-Euphrates, Indus, Ganges-Brahmaputra, and Irrawady rivers. The surface waters of the ocean are generally warm, although close to Antarctica pack ice and icebergs are found.

The southwest monsoon draws moisture from the Indian Ocean and drops heavy rainfall on the Indian subcontinent and Southeast Asia. The Indian Ocean has two water circulation systems - a regular counterclockwise southern system (South Equatorial Current, Mozambique Current, West Wind Drift, West Australian Current) and a northern system, the Monsoon Drift, whose currents are directly related to the seasonal shift of monsoon winds. 

                                 Indian Ocean Islands