Adelaide is the capital and most populous city of the Australian state of South Australia, and is the fifth-largest city in Australia, with a population of more than 1.1 million. It is a coastal city situated on the eastern shores of Gulf St. Vincent, on the Adelaide Plains, north of the Fleurieu Peninsula, between the Gulf St. Vincent and the low-lying Mount Lofty Ranges. It is roughly 20 km (12 mi) from the coast to the foothills but sprawls 90 km (56 mi) from Gawler at its northern extent to Sellicks Beach in the south.

Named in honour of Queen Adelaide who was born in Germany, the consort of King William IV, the city was founded in 1836 as the planned capital for the only freely-settled British province in Australia. Colonel William Light, one of Adelaide's founding fathers, designed the city and chose its location close to the River Torrens in the area originally inhabited by Indigenous Australians of the Kaurna tribe. Light's design set out Adelaide in a grid layout, interspaced by wide boulevards and large public squares, and entirely surrounded by parkland. Early Adelaide was shaped by religious freedom and a commitment to political progressivism and civil liberties, which led to world-first reforms.

As South Australia's seat of government and commercial centre, Adelaide is the site of many governmental and financial institutions. Most of these are concentrated in the city centre along the cultural boulevard of North Terrace, King William Street and in various districts of the metropolitan area.

Today, Adelaide is noted for its many festivals and sporting events, its food, wine and culture, its long beachfronts, and its large defence and manufacturing sectors. It continues to rank highly as a livable city, being in the Top 10 in The Economist's World's Most Livable Cities index.

Adelaide is located north of the Fleurieu Peninsula, on the Adelaide Plains between the Gulf St Vincent and the low-lying Mount Lofty Ranges. The city stretches 20 km (12 mi) from the coast to the foothills, and 90 km (56 mi) from Gawler at its northern extent to Sellicks Beach in the south. According to the Australian Bureau of Statistics, the Adelaide Metropolitan Region has a total land area of 870 km2 (340 sq mi), and is at an average elevation of 50 metres (160 ft) above sea level. Mount Lofty is located east of the Adelaide metropolitan region in the Adelaide Hills at an elevation of 727 metres (2,390 ft). It is the tallest point of the city and in the state south of Burra.

Much of Adelaide was bushland before British settlement, with some variation - swamps and marshlands were prevalent around the coast. However, much of the original vegetation has been cleared with what is left to be found in reserves such as the Cleland Conservation Park and Belair National Park. A number of creeks and rivers flow through the Adelaide region. The largest are the Torrens and Onkaparinga catchments. Adelaide relies on its many reservoirs for water supply, with Mount Bold Reservoir and Happy Valley Reservoir together supplying around 50% of Adelaide's requirements.

The main sports played professionally in Adelaide are Australian rules football, Association football and cricket. Adelaide is the home of two Australian Football League teams: the Adelaide Crows and Port Adelaide Power. A local Australian rules football league, the SANFL, is made up of nine teams from around Adelaide.

Most large sporting events take place at either AAMI Stadium or the historic Adelaide Oval, home of the Southern Redbacks cricket team. Adelaide hosts an international cricket test every summer, along with a number of One Day International cricket matches. Memorial Drive Park, adjacent to the Adelaide Oval, used to host the Adelaide International, a major men's tennis tournament in the lead-up to the Australian Open before the tournament was moved to Brisbane in 2009.

Adelaide's professional Association football team, Adelaide United, play in the A-League. Founded in 2003, their home ground is Hindmarsh Stadium, which has a capacity of 16,500 and is one of the few purpose-built soccer stadia in Australia. In 2008 the Cronulla Sharks, an Australian NRL franchise, and the South Australian Government announced a 3 year contract in which the Sharks will play a single home game each season at Hindmarsh Stadium.

The Adelaide 36ers and the Adelaide Lightning play in national basketball competitions, with home games at the Distinctive Homes Dome. The Adelaide Thunderbirds play in the trans-Tasman netball competition, with home games at ETSA Park.

Adelaide hosts the Tour Down Under bicycle race, the largest cycling event outside Europe and the only event with UCI ProTour status.

The Australian Grand Prix for Formula One racing was hosted by Adelaide from 1985 to 1995 on a street circuit in the city's eastern parklands. The Grand Prix became a source of pride and losing the event to Melbourne in a surprise announcement left a void that has since been filled with the highly successful Clipsal 500 for V8 Supercar racing, held on a modified version of the same street circuit. The Classic Adelaide, a rally of classic sporting vehicles, is also held in the city and its surrounds.

The World Solar Challenge race attracts teams from around the world, most of which are fielded by universities or corporations although some are fielded by high schools. The race has a 20-year history spanning nine races, with the inaugural event taking place in 1987.