The most satisfactory way of classifying the many hundreds of Indian tribes living in what is now Brazil when the Europeans arrived in 1500 is by language group and by geography and habitat. There were four main language families (in probable order by population): Tupi (or Tupi-Guarani), Gê, Carib and Aruak (Arawak). (Other language families were only represented at the edge of the frontiers of modern Brazil: Xirianá and Tukano in the north-west, Panoan and Paezan in the west, Guaicuruan and Charrua in the south. Some surviving tribal languages are classified as isolated, or only slightly linked to the main language trunks: Nambicuara (Nambikwara), Bororo, Karajá, Mura, Aripaktsá, and doubtless many others among the hundreds of tribes who died out before their speech was studied by linguists.)

The Tupi-Guaraní were established along most of the Atlantic seaboard. They may have originated in the Andes foothills or the plateau of the middle Paraguay and Paraná rivers and been in the process of a gradual northwards invasion of the Brazilian coast. Other Tupispeaking tribes occupied the south bank of the Amazon river, moving up the southern tributaries near its mouth, and upstream on the main river almost to the modern Peruvian border. The Gê occupied the vast, relatively open, plateau of central Brazil. The Gê may be descendants of the original inhabitants of Brazil – the oldest human fossil finds at Lagôa Santa in Minas Gerais, which are over 10,000 years old, correspond physically to modern Gê types. These central Gê-speaking tribes cover an enormous arc of land from Maranhāo to the upper Paraguay.