The Australasian zone is an ecological region that is coincident, but not synonymous (by some definitions), with the geographic region of Australasia. The ecozone includes Australia, the island of New Guinea (including Papua New Guinea and the Indonesian province of Papua), and the eastern part of the Indonesian archipelago, including the island of Sulawesi, the Moluccan islands (the Indonesian provinces of Maluku and North Maluku) and islands of Lombok, Sumbawa, Sumba, Flores, and Timor, often known as the Lesser Sundas. The Australasian ecozone also includes several Pacific island groups, including the Bismarck Archipelago, Vanuatu, the Solomon Islands, and New Caledonia. New Zealand and its surrounding islands are a distinctive sub-region of the Australasian ecozone. The rest of Indonesia is part of the Indomalayan ecozone.

From an ecological perspective the Australasia ecozone is a distinct region with a common geologic and evolutionary history and a great many unique flora and fauna. In this context, Australasia is limited to Australia, New Guinea, New Zealand, New Caledonia, and neighbouring islands, including the Indonesian islands from Lombok and Sulawesi eastward. The biological dividing line from the Indomalaya ecozone of tropical Asia is the Wallace Line – Borneo and Bali lie on the western, Asian side.