In anthropology, a tribe is a human social group. Exact definitions of what constitutes a tribe vary among anthropologists. The concept is often contrasted with other social groups concepts, such as nations, states, and forms of kinship.

In some places, such as India and North America, tribes are polities that have been granted legal recognition and limited autonomy by the national or federal government.

The word tribe first occurs in English in 12th-century Middle English-literature, in reference to the twelve tribes of Israel. The Middle English word is derived from Old French tribu and, in turn, from Latin tribus (plural tribūs), in reference to a supposed tripartite division of the original Roman state along ethnic lines, into tribūs known as the Ramnes (or Ramnenses), Tities (or Titienses), and Luceres, corresponding, according to Marcus Terentius Varro, to the Latins, Sabines and Etruscans respectively. The Ramnes were named after Romulus, leader of the Latins, Tities after Titus Tatius, leader of the Sabines, and Luceres after Lucumo, leader of an Etruscan army that had assisted the Latins. In 242–240 BC, the Tribal Assembly (comitia tributa) in the Roman Republic included 35 tribes (four "urban tribes" and 31 "rural tribes"). According to Livy, the three "tribes" were squadrons of cavalry, rather than ethnic divisions.

The term's ultimate etymology is uncertain, perhaps from the Proto-Indo-European roots tri- ("three") and bhew ("to be"). The classicist Gregory Nagy says,^[1] citing the linguist Émile Benveniste,^[2] Umbrian]] * (equivalent of the Latin ) is apparently derived from a combination of* ond element is cognate with the Greek root phúō φύω “to bring forth” and the Greek phulē φυλή "clan, race, people" (plural phylai φυλαί). The Greek polis ("state" or "city") was, like the Roman state, often divided into phylai.

In Europe during the late medieval era, the Bible was written mostly in New Latin and instead of tribus the word phyle was used, derived from the Greek phulē. In the historical sense, "tribe", "race" and "clan" have often been used interchangeably.

The term and concept of a tribe is controversial among anthropologists and other academics active in the social sciences. The term tribe was in common use in the field of anthropology until the late 1950s and 1960s, during which time scholars began to reassess its utility. In 1970, anthropologist J. Clyde Mitchell writes:

Writing in 2013, scholar Matthew Ortoleva notes that "like the word Indian, * [t]ribe* is a word that has connotations of colonialism."^[4]

Survival International says "It is important to make the distinction between tribal and indigenous because tribal peoples have a special status acknowledged in international law as well as problems in addition to those faced by the wider category of indigenous peoples."^[5]

Considerable debate has accompanied efforts to define and characterize tribes.

When scholars use the term, they may perceive differences between pre-state tribes and contemporary tribes; there is also general controversy over cultural evolution and colonialism. In the popular imagination, tribes reflect a way of life that predates, and is more natural than that in modern states. Tribes can also refer to primordial social groups that are clearly bounded, homogeneous, parochial, and stable. Tribes are an organization among families (including clans and lineages), which generates a social and ideological basis for solidarity that is in some way more limited than that of an "ethnic group" or of a "nation". Anthropological and ethnohistorical research has challenged all of these notions.

Anthropologist Elman Service presented a system of classification for societies in all human cultures, based on the evolution of social inequality and the role of the state. This system of classification contains four categories:

In his 1975 study, The Notion of the Tribe, anthropologist Morton H. Fried provided numerous examples of tribes that encompassed members who spoke different languages and practiced different rituals, or who shared languages and rituals with members of other tribes. Similarly, he provided examples of tribes in which people followed different political leaders, or followed the same leaders as members of other tribes. He concluded that tribes in general are characterized by fluid boundaries and heterogeneity, are not parochial, and are dynamic.^[6]

Fried proposed that most contemporary tribes do not have their origin in pre-state tribes, but rather in pre-state bands.

Such "secondary" tribes, he suggested, developed as modern products of state expansion.

Bands comprise small, mobile, and fluid social formations with weak leadership. They do not generate surpluses, pay no taxes, and support no standing army. Fried argued that secondary tribes develop in one of two ways. First, states could set them up as means to extend administrative and economic influence in their hinterland, where direct political control costs too much. States would encourage (or require) people on their frontiers to form more clearly bounded and centralized polities, because such polities could begin producing surpluses and taxes, and would have a leadership responsive to the needs of neighboring states (the so-called "scheduled" tribes of the United States or of British India provide good examples of this). Second, bands could form "secondary" tribes as a means to defend against state expansion. Members of bands would form more clearly bounded and centralized polities, because such polities could begin producing surpluses that could support a standing army that could fight against states, and they would have a leadership that could co-ordinate economic production and military activities.

Archaeologists continue to explore the development of pre-state tribes. Current research suggests that tribal structures constituted one type of adaptation to situations providing plentiful yet unpredictable resources. Such structures proved flexible enough to coordinate production and distribution of food in times of scarcity, without limiting or constraining people during times of surplus.