Australia, officially the Commonwealth of Australia, is a country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. Australia is the largest country by area in Oceania and the world's sixth-largest country. Australia is the oldest, flattest, and driest inhabited continent, with the least fertile soils. It is a megadiverse country, and its size gives it a wide variety of landscapes and climates, with deserts in the centre, tropical rainforests in the north-east, tropical savannas in the north, and mountain ranges in the south-east.

The ancestors of Aboriginal Australians began arriving from south-east Asia 50,000 to 65,000 years ago, during the last glacial period. They settled the continent and had formed approximately 250 distinct language groups by the time of European settlement, maintaining some of the longest known continuing artistic and religious traditions in the world. Australia's written history commenced with European maritime exploration. The Dutch were the first known Europeans to reach Australia, in 1606. British colonisation began in 1788 with the establishment of the penal colony of New South Wales. By the mid-19th century, most of the continent had been explored by European settlers and five additional self-governing British colonies were established, each gaining responsible government by 1890. The colonies federated in 1901, forming the Commonwealth of Australia. This continued a process of increasing autonomy from the United Kingdom, highlighted by the Statute of Westminster Adoption Act 1942, and culminating in the Australia Acts of 1986.

Australia is a federal parliamentary constitutional monarchy comprising six states and ten territories: the states of New South Wales, Victoria, Queensland, Tasmania, South Australia and Western Australia; the major mainland Australian Capital Territory and Northern Territory; and other minor or external territories. Its population of nearly 27 million is highly urbanised and heavily concentrated on the eastern seaboard. Canberra is the nation's capital, while its most populous cities are Sydney, Melbourne, Brisbane, Perth and Adelaide, which each possess a population of at least one million inhabitants. Australian governments have promoted multiculturalism since the 1970s. Australia is culturally diverse and has one of the highest foreign-born populations in the world. Its abundant natural resources and well-developed international trade relations are crucial to the country's economy, which generates its income from various sources: predominantly services (including banking, real estate and international education) as well as mining, manufacturing and agriculture. It ranks highly for quality of life, health, education, economic freedom, civil liberties and political rights.