Oceania (UK: , US: (listen), ) is a geographical region that is described as a continent in some parts of the world. It includes Australasia, Melanesia, Micronesia, and Polynesia. Spanning the Eastern and Western Hemispheres, Oceania is estimated to have a land area of 8,525,989 square kilometres (3,291,903 sq mi) and a population of around 44.4 million as of 2022. Oceania is described as a geographical region in most of the English-speaking world, but outside of the English-speaking world, Oceania is described as one of the continents. In this model of the world, Australia is only seen as an island nation contained inside of the continent of Oceania, and not a continent by itself. When compared to the other continents, Oceania is the smallest in land area and the second least populated after Antarctica.

Oceania has a diverse mix of economies from the highly developed and globally competitive financial markets of Australia, French Polynesia, Hawaii, New Caledonia, and New Zealand, which rank high in quality of life and Human Development Index, to the much less developed economies of Kiribati, Papua New Guinea, Tuvalu, Vanuatu, and Western New Guinea, while also including medium-sized economies of Pacific islands such as Fiji, Palau, and Tonga. The largest and most populous country in Oceania is Australia, and the largest city is Sydney. Puncak Jaya in Highland Papua, Indonesia, is the highest peak in Oceania at 4,884 m (16,024 ft).

The first settlers of Australia, New Guinea, and the large islands just to the east arrived more than 60,000 years ago. Oceania was first explored by Europeans from the 16th century onward. Portuguese explorers, between 1512 and 1526, reached the Tanimbar Islands, some of the Caroline Islands and west New Guinea. Spanish and Dutch explorers followed, then British and French. On his first voyage in the 18th century, James Cook, who later arrived at the highly developed Hawaiian Islands, went to Tahiti and followed the east coast of Australia for the first time.

The arrival of European settlers in subsequent centuries resulted in a significant alteration in the social and political landscape of Oceania. The Pacific theatre saw major action during the Second World War, mainly between Allied powers the United States, Philippines (a U.S. Commonwealth at the time) and Australia, and Axis power Japan. The rock art of Aboriginal Australians is the longest continuously practiced artistic tradition in the world. Most Oceanian countries are multi-party representative parliamentary democracies, with tourism being a large source of income for the Pacific Islands nations.