Melanesia (from Greek: μέλας black, νῆσος island) is a region extending from the western side of the East Pacific to the Arafura Sea, north and north-east of Australia. The term was first used by Jules Dumont d'Urville in 1832 to denote an ethnic and geographical grouping of islands distinct from Polynesia and Micronesia.

Today d'Urville's racial classification is known to be inaccurate because it obscures Melanesia's very great cultural, linguistic, and genetic diversity and combines two quite distinct groups, the Austronesians (who have a much wider distribution than just Melanesia) and the Papuans (who themselves comprise a number of separate groups). A further complication is that the term Melanesian is sometimes used to refer solely to the Austronesian peoples of that region, especially when contrasting them with the Polynesians and Micronesians (both of which groups are also Austronesian).

In contrast, the geopolitical conception of Melanesia is widely used. For example, the Melanesian Spearhead Group Preferential Trade Agreement is a regional trade treaty governing the states of Vanuatu, Solomon Islands, Papua New Guinea and Fiji. People of Melanesian countries often talk about the Melanesian way, which people of the region see as a distinctively Melanesian set of cultural values and behaviour. 'Melanesia' is also current as a geographic term, to refer to the area when national, ethnic and linguistic distinctions are not relevant.