Sydney ( (listen) SID-nee) is the capital city of the state of New South Wales, and the most populous city in both Australia and Oceania. Located on Australia's east coast, the metropolis surrounds Sydney Harbour and extends about 70 km (43.5 mi) towards the Blue Mountains to the west, Hawkesbury to the north, the Royal National Park and Macarthur to the south and south-west. Greater Sydney is made up of 658 suburbs, spread across 33 local government areas. Residents of the city are known as "Sydneysiders". The estimated population in June 2021 was over 5.2 million, meaning the city is home to approximately 66% of the state's population. Nicknames of the city include the 'Emerald City' and the 'Harbour City'.

Aboriginal Australians have inhabited the Greater Sydney region for at least 30,000 years, and Aboriginal engravings and cultural sites are common throughout Greater Sydney. The traditional custodians of the land on which modern Sydney stands are the clans of the Darug, Dharawal and Eora peoples.

During his first Pacific voyage in 1770, James Cook charted the eastern coast of Australia, making landfall at Botany Bay. In 1788, the First Fleet of convicts, led by Arthur Phillip, founded Sydney as a British penal colony, the first European settlement in Australia. After World War II, Sydney experienced mass migration and by 2021 over 40 per cent of the population was born overseas. Foreign countries of birth with the greatest representation are Mainland China, India, England, Vietnam and the Philippines.

Despite being one of the most expensive cities in the world, Sydney frequently ranks in the top ten most liveable cities in the world. It is classified as an Alpha global city by the Globalization and World Cities Research Network, indicating its influence in the region and throughout the world. Ranked eleventh in the world for economic opportunity, Sydney has an advanced market economy with strengths in finance, manufacturing and tourism. Established in 1850, the University of Sydney was Australia's first university and is regarded as one of the world's leading universities.

Sydney has hosted major international sporting events such as the 2000 Summer Olympics. The city is among the top fifteen most-visited cities in the world, with millions of tourists coming each year to see the city's landmarks. The city has over 1,000,000 ha (2,500,000 acres) of nature reserves and parks, and its notable natural features include Sydney Harbour and Royal National Park. The Sydney Harbour Bridge and the World Heritage-listed Sydney Opera House are major tourist attractions. Central Station is the hub of Sydney's rail network, and the main passenger airport serving the city is Kingsford Smith Airport, one of the world's oldest continually operating airports.