High Quality Content by WIKIPEDIA articles! Australia officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent (the world's smallest),the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. Neighbouring countries include Indonesia, East Timor, and Papua New Guinea to the north, the Solomon Islands, Vanuatu, and New Caledonia to the north-east, and New Zealand to the southeast.