Geographically Melanesia incorporates the southern Pacific Ocean islands north and northeast of Australia, from New Guinea on the west to Fiji on the east. Over 5000 islands and islets, with a land area totaling about 386K sq. mi., cover over 500K square miles of water from the South Pacific Ocean to the Coral Sea, Solomon Sea, Bismarck Sea, Arafura Sea, Haimahera Sea, Ceram Sea, Banda Sea and Molucca Sea.
In order of size, the island groups/countries that make up Melanesia are:
Island of New Guinea 303,000 sq. mi.; population 7.5 million
Second largest island in the world (after Greenland), split in two politically the eastern half of the island being Papua New Guinea, formerly a territory of Australia, now an independent country since 1975; and the western half of the island, formerly a Dutch colony, now made up of two provinces of Indonesia (Papua and West Papua). Known as one of the most linguistically diverse regions of the world, with nearly a thousand different tribal groups, some of which are still considered uncontacted. Numerous opportunities for adventure tours and eco tours. Popular tourist activities include trekking, mountain climbing, surfing, snorkeling, scuba diving, canoeing/kayaking, caving, wildlife and bird-watching, visiting World War II historical sites, and learning about the local tribes and cultures.
Islands of Papua New Guinea
Besides constituting half of the island of New Guinea (as described above), the country of Papua New Guinea has several island groups that belong to it. There is not much in the way of tourism facilities on most of these islands; so most tourists enjoy them through island-hopping live-aboard yacht or cruise tours from the main island of New Guinea. The islands include: 1) Bismarck Archipelago 19,000 sq. mi.; population 472,000; located to the northeast of the main island, part of the Islands Region, an archipelago of around 200 islands surrounding the Bismarck Sea, the largest of these islands is New Britain. 2) The Autonomous Region of Bougainville (previously known as the North Solomons) 3600 sq. mi.; population 175,000; includes the main island of Bougainville plus around 200 outlying islands. 3) The Milne Bay Province, at the southeast tip of Papua New Guinea, includes several island groups in the Solomon Sea totaling more than 600 islands, about 160 of which are inhabited. These include: the Amphlett Islands, the dEntrecasteaux Islands, the Trobriand Islands, the Louisiade Archipelago, and Woodlark Island.
Maluku Islands 29,000 sq. mi.; population 2,000,000
Also known as the Moluccas, and historically known as the Spice Islands for the growing of nutmeg and cloves; an Indonesian archipelago of over 1000 islands and islets, located just west of New Guinea and east of the main part of Indonesia. Minimal tourist facilities, but known for good snorkeling.
Solomon Islands 11,000 sq. mi.; population 585,000
A sovereign state (constitutional monarchy), previously a British protectorate, east of Papua New Guinea; bordered on the south by the Solomon Sea and the Coral Sea and on the north by the South Pacific Ocean; made up of nearly 1000 islands and islets with 3300 miles of coastline; mostly rugged mountains with some low coral atolls. Limited tourist facilities but popular tourist activities include scuba diving, snorkeling, World War II historical tours, wildlife viewing and photography.
Read more here:
List of the Islands of Melanesia