South Auckland (Māori: Te Tonga o Tāmaki Makaurau or Māori: Tāmaki ki te Tonga) is one of the major geographical regions of Auckland, the largest city in New Zealand. The area is south of the Auckland isthmus, and on the eastern shores of the Manukau Harbour. The area has been populated by Tāmaki Māori since at least the 14th century, and has important archaeological sites, such as the Ōtuataua stonefield gardens at Ihumātao, and Māngere Mountain, a former pā site important to Waiohua tribes.

The area was primarily farmland until the mid-20th century, when the construction of the Auckland Southern Motorway led to major suburban development, and the establishing of Manukau City, which was later amalgamated into Auckland. Large-scale state housing areas were constructed in the 1960s and 1970s, which led to significant Urban Māori and Pasifika communities developing in the area. The presence of 165 different ethnicities makes South Auckland one of the most diverse places in New Zealand. It is Auckland's most socio-economically deprived area.

South Auckland is not a strictly defined area. It primarily refers to the western and central parts of the former Manukau City, which existed between 1989 and 2010, and surrounding areas of Franklin. Major areas of South Auckland include Māngere, Manukau, Manurewa, Ōtāhuhu, Ōtara, Papakura and Papatoetoe. A strict definition sometimes used for South Auckland includes just the Māngere-Ōtāhuhu, Manurewa, Ōtara-Papatoetoe, Papakura local board areas.

The term South Auckland was first used in the 1880s, to refer to areas of the southern Auckland Province, such as Cambridge, Ngāruawāhia, Te Awamutu, or Hamilton. The first references to modern South Auckland come from 1962, in discussions for the creation of Manukau City. The term began developing negative connotations in the 1970s, with non-residents associating the term with deprivation, crime and violence. From 1989, many organisations began using the term Counties Manukau as an alternative way to describe South Auckland.

The name South Auckland is often used imprecisely by the press or politicians, to describe lower socio-economic areas south of the Auckland City Centre. Some areas of the Auckland isthmus occasionally referred to as South Auckland are Onehunga, Penrose, Mount Wellington, and Panmure. Some Howick ward suburbs to the East often get confused by being called South Auckland, including Flat Bush and East Tāmaki. Towns south of Auckland are also often referred to as South Auckland, including Pukekohe and Waiuku, and occasionally some towns in the northern Waikato Region, such as Pōkeno and Tuakau.

South Auckland is an area on the eastern shores of the Manukau Harbour, and the upper headwaters of the Tāmaki River. Many features of the Auckland volcanic field are found in South Auckland, such as Māngere Mountain, Matukutūreia and the Pukaki Lagoon. Many of the mountains of South Auckland have been quarried, such as Matukutūruru, Maungataketake and Ōtara Hill (either entirely or partially). Some of the northern-most features of the older South Auckland volcanic field can be found in the area, such as Pukekiwiriki and the Hūnua Falls.

Both the Manukau Harbour and the Tāmaki River are drowned river valley systems. The Manukau Harbour formed between 3 and 5 million years ago when tectonic forces between the Pacific Plate and Australian Plate uplifted the Waitākere Ranges and subsided the Manukau Harbour. It began as an open bay, eventually forming as a sheltered harbour as the Āwhitu Peninsula developed at the harbour's mouth. Over the last two million years, the harbour has cycled between periods of being a forested river valley and a flooded harbour, depending on changes in the global sea level. The present harbour formed approximately 8,000 years ago, after the Last Glacial Maximum.

Historically, much of inland South Auckland was composed of wetlands. Many areas of remnant native bush are found in South Auckland, such as the taraire forest at Kirk's Bush in Papakura, and areas of the Auckland Botanic Gardens in Manurewa.