Johannesburg ( joh-HAN-iss-burg, US also -⁠HAHN-, Afrikaans: [juəˈɦanəsbœrχ]; Zulu and Xhosa: eGoli [ɛˈɡɔːli]), colloquially known as Jozi, Joburg, or "The City of Gold", is the most populous city in South Africa, classified as a megacity, and is one of the 100 largest urban areas in the world. According to Demographia, the Johannesburg–Pretoria urban area (combined because of strong transport links that make commuting feasible) is the 26th-largest in the world in terms of population, with 14,167,000 inhabitants. It is the provincial capital and largest city of Gauteng, which is the wealthiest province in South Africa. Johannesburg is the seat of the Constitutional Court, the highest court in South Africa. Most of the major South African companies and banks have their head offices in Johannesburg. The city is located in the mineral-rich Witwatersrand range of hills and is the centre of large-scale gold and diamond trade.

The city was established in 1886 following the discovery of gold on what had been a farm. Due to the extremely large gold deposit found along the Witwatersrand, within ten years, the population had grown to 100,000 inhabitants. A separate city from the late 1970s until 1994, Soweto is now part of Johannesburg. Originally an acronym for "South-Western Townships", Soweto originated as a collection of settlements on the outskirts of Johannesburg, populated mostly by native African workers from the gold mining industry. Soweto, although eventually incorporated into Johannesburg, had been separated as a residential area for blacks only (no whites allowed), who were not permitted to live in other White designated suburbs of Johannesburg. Lenasia is predominantly populated by English-speaking South Africans of Indian descent. These areas were designated as non-white areas in accordance with the segregationist policies of the South African government known as apartheid. It was one of the host cities of the official tournament of the 2010 FIFA World Cup—and it hosted the final.

The metropolis is an alpha global city as listed by the Globalization and World Cities Research Network. In 2019, the population of the city of Johannesburg was 5 635 127, making it the most populous city in South Africa. In the same year, the population of Johannesburg's urban agglomeration was put at 8 000 000. Land area of the municipal city (1,645 km² or 635 sq mi) is large in comparison with those of other major cities, resulting in a moderate population density of 2,364 per square kilometre (6,120/sq mi).