Sydney () is the most populous city in Australia, with a metropolitan area population of approximately 4.28 million (2006 estimate). It is the state capital of New South Wales, and was the site of the first British colony in Australia. It was established in 1788 at Sydney Cove by Arthur Phillip, leader of the First Fleet from Britain. A resident of the city is referred to as a Sydneysider.

Sydney is situated on Australia's south-east coast. The city is built around Port Jackson, which includes Sydney Harbour, leading to the city's nickname, "the Harbour City". It is noted for the Sydney Opera House and the Harbour Bridge, and its beaches. The metropolitan area is surrounded by national parks, and contains many bays, rivers and inlets. It is listed as a beta world city by the Loughborough University group's 1999 inventory. The city has hosted international sporting, political and cultural events, including the 1938 British Empire Games, 2000 Summer Olympics and the 2003 Rugby World Cup. In September 2007, the city hosted the leaders of the 21 APEC economies for APEC Australia 2007, and in July 2008 hosted World Youth Day 2008. The main airport serving Sydney is Sydney Airport.

Sydney is one of the most multicultural cities in the world, which reflects its role as a major destination for immigrants to Australia. According to the Mercer cost of living survey, Sydney is Australia's most expensive city, and the 15th most expensive in the world.

: For a topic outline on this subject, see List of basic Australia topics. For other uses, see Australia (disambiguation).

Australia, officially the Commonwealth of Australia, is a country in the southern hemisphere comprising the mainland of the world's smallest continent, the major island of Tasmania and numerous other 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 northeast, and New Zealand to the southeast. Australia is the only single country to occupy an entire continent.

The Australian mainland has been inhabited for more than 42,000 years by indigenous Australians.Both Australian Aborigines and Europeans Rooted in Africa - 50,000 years ago After sporadic visits by fishermen from the north and then European discovery by Dutch explorers in 1606,MacKnight, CC (1976). The Voyage to Marege: Macassan Trepangers in Northern Australia. Melbourne University Press the eastern half of Australia was later claimed by the British in 1770 and initially settled through penal transportation to the colony of New South Wales, commencing on 26 January 1788. As the population grew and new areas were explored, another five largely self-governing Crown Colonies were established during the 19th century.

On 1 January 1901, the six colonies became a federation, and the Commonwealth of Australia was formed. Since federation, Australia has maintained a stable liberal democratic political system and remains a Commonwealth realm. The capital city is Canberra, located in the Australian Capital Territory (ACT). The population is just over 21.3 million, with approximately 60% of the population concentrated in and around the mainland state capitals of Sydney, Melbourne, Brisbane, Perth and Adelaide.