Iwi (Māori pronunciation: [ˈiwi]) are the largest social units in New Zealand Māori society. The Māori language word iwi means "people" or "nation", and is often translated as "tribe", or a confederation of tribes. The word iwi is both singular and plural in Māori. Most Māori in pre-European times gave their primary allegiance to relatively small groups such as hapū ("sub-tribe") and whānau ("family").
Iwi groups trace their ancestry to the original Polynesian migrants who, according to tradition, arrived from Hawaiki. Some iwi cluster into larger groupings based on genealogical tradition, known as waka (literally: "canoes", with reference to the original migration voyages), but these super-groupings generally serve symbolic rather than practical functions. Each iwi has a number of hapū ("sub-tribes"). For example, the Ngāti Whātua iwi has hapū including Te Uri-o-Hau, Te Roroa, Te Taou, and Ngāti Whātua ki Ōrākei.
In modern-day New Zealand, iwi groups may exercise significant political power in the recovery and management of land and of other assets. (Note for example the 1997 settlement between the New Zealand Government and Ngāi Tahu, compensating that iwi for various losses of the rights guaranteed under the Treaty of Waitangi of 1840). Iwi affairs can have a very real impact on New Zealand politics and society. A 2004 attempt by some iwi to test in court their ownership of the seabed and foreshore areas, polarised public opinion (see New Zealand foreshore and seabed controversy).