Adelaide ( AD-il-ayd; Kaurna: Tarntanya pronounced [ˈd̪̥aɳɖaɲa]) is the capital city of South Australia, the state's largest city and the fifth-most populous city in Australia. "Adelaide" may refer to either Greater Adelaide (including the Adelaide Hills) or the Adelaide city centre. The demonym Adelaidean is used to denote the city and the residents of Adelaide. The Traditional Owners of the Adelaide region are the Kaurna people. The area of the city centre and surrounding Park Lands is called Tarndanya in the Kaurna language.

Adelaide is situated on the Adelaide Plains north of the Fleurieu Peninsula, between the Gulf St Vincent in the west and the Mount Lofty Ranges in the east. Its metropolitan area extends 20 km (12 mi) from the coast to the foothills of the Mount Lofty Ranges, and stretches 96 km (60 mi) from Gawler in the north to Sellicks Beach in the south.

Adelaide was consistently ranked in the world's 10 most liveable cities through the 2010s by The Economist Intelligence Unit. In June 2021, The Economist ranked Adelaide the third most liveable city in the world, behind Auckland and Osaka. In June 2023, Adelaide was ranked the twelfth most liveable city in the world by the Economist Intelligence Unit.

In December 2021, Adelaide was named the world's second National Park City, after the state government had lobbied for this title.

It was ranked the most liveable city in Australia by the Property Council of Australia, based on surveys of residents' views of their own city, between 2010 and 2013, dropping to second place in 2014.