Tanzania is extremely heterogeneous, with more than 120 different indigenous African peoples as well as small groups of Asians and Europeans. As early as 5000 BC, San-type hunting bands colonised the nation. The Sandawe hunters of northern Tanzania are thought to be their descendants. By 1000 BC, agriculture and pastoral practices were being introduced through the migration of Cushitic people from Ethiopia. The Iraqw, Mbugu, Gorowa, and Burungi have Cushitic origins. About AD 500, iron-using Bantu agriculturalists coming from the west and south started displacing or absorbing the San hunters and gatherers; at roughly the same time, Nilotic pastoralists entered the area from the southern Sudan. Today the majority of Tanzanians are of Bantu descent; the Sukuma constitute the largest group, and others are the Nyamwezi, Hehe, Nyakyusa, Makonde, Yao, Haya, Chaga, Gogo, and Ha. Nilotic peoples are described by the Masai, Arusha, Samburu, and Baraguyu. No one group has been politically or culturally dominant, although the tribes that were subject to Christian missionary determine and Western education during the colonial time (notably the Chaga and Haya) are now disproportionately described in the government administration and cash economy.

Each ethnic group has its own language, but the national language is Kiswahili, a Bantu-based tongue with strong Arabic borrowings.