The Kongo have long occupied all of Bas-Zaïre Region. Most but not all of these peoples, together with substantial numbers in Angola and smaller numbers in Congo, were originally inhabitants of the kingdom of the Kongo encountered by the Portuguese in the late fifteenth century. For all practical purposes, that kingdom had disintegrated into a number of small chiefdoms by the early seventeenth century. The end of the kingdom's political power did not preclude the continuing spread of Kongo influence, however, and some groups may have become Kongo in culture later.

Given the size of the population and the territorial range of the Kongo, much dialectical variation in their language has developed, to the point that some dialects are barely mutually intelligible. There are similar variations in other aspects of culture. From the seventeenth century until the arrival of the Belgians, there were shifting combinations of smaller chiefdoms into larger entities under the domination of one or another chief, the power of a dominant chief often reflecting his easier access to or more effective exploitation of the slave and ivory trade of the period. The hierarchies thus established were usually ephemeral. In the end, the effective units were the clans, their larger constituent units called by anthropologist Wyatt MacGaffey houses (the units controlling land), and lineages, rather shallow units. All of these units were based on matrilineal descent. Although each unit had a head, authority was shared with persons both inside and outside the unit in a complex fashion.

Because of their early contact with Europeans, the Kongo were among the groups early and heavily influenced by Roman Catholic and Protestant missionaries and by the schools established by them. The Roman Catholics placed particular emphasis on the traditions of the Kongo as they understood them and in turn communicated these reconstructed traditions to their students. The complex interaction of myth, competition, and the ambition of some leaders of Kongo origin as the prospect of independence loomed made the Kongo the largest single group to define themselves in ethnic terms for political purposes in the late 1950s and one of the few to develop an articulate ethnic ideology (see The Rise of Militant Ethnicity: Abako , ch. 1).

Data as of December 1993