Indonesia, country located off the coast of mainland Southeast Asia in the Indian and Pacific oceans. It is an archipelago that lies across the Equator and spans a distance equivalent to one-eighth of Earth’s circumference. Its islands can be grouped into the Greater Sunda Islands of Sumatra (Sumatera), Java (Jawa), the southern extent of Borneo (Kalimantan), and Celebes (Sulawesi); the Lesser Sunda Islands (Nusa Tenggara) of Bali and a chain of islands that runs eastward through Timor; the Moluccas (Maluku) between Celebes and the island of New Guinea; and the western extent of New Guinea (generally known as Papua). The capital, Jakarta, is located near the northwestern coast of Java. In the early 21st century Indonesia was the most populous country in Southeast Asia and the fourth most populous in the world.

Indonesia was formerly known as the Dutch East Indies (or Netherlands East Indies). Although Indonesia did not become the country’s official name until the time of independence, the name was used as early as 1884 by a German geographer; it is thought to derive from the Greek indos, meaning “India,” and nesos, meaning “island.” After a period of occupation by the Japanese (1942–45) during World War II, Indonesia declared its independence from the Netherlands in 1945. Its struggle for independence, however, continued until 1949, when the Dutch officially recognized Indonesian sovereignty. It was not until the United Nations (UN) acknowledged the western segment of New Guinea as part of Indonesia in 1969 that the country took on its present form. The former Portuguese territory of East Timor (Timor-Leste) was incorporated into Indonesia in 1976. Following a UN-organized referendum in 1999, however, East Timor declared its independence and became fully sovereign in 2002.

The Indonesian archipelago represents one of the most unusual areas in the world: it encompasses a major juncture of Earth’s tectonic plates, spans two faunal realms, and has for millennia served as a nexus of the peoples and cultures of Oceania and mainland Asia. These factors have created a highly diverse environment and society that sometimes seem united only by susceptibility to seismic and volcanic activity, close proximity to the sea, and a moist, tropical climate. Nevertheless, a centralized government and a common language have provided Indonesia with some sense of unity. Furthermore, in keeping with its role as an economic and cultural crossroads, the country is active in numerous international trade and security organizations, such as ASEAN, OPEC, and the UN.