An ethnic group is a group of people whose members identify with each other, through a common heritage that is real or assumed- sharing cultural characteristics This shared heritage may be based upon putative common ancestry, history, kinship, religion, language, shared territory, nationality or physical appearance. Members of an ethnic group are conscious of belonging to an ethnic group; moreover ethnic identity is further marked by the recognition from others of a group's distinctiveness.

According to "Challenges of Measuring an Ethnic World: Science, politics, and reality", a conference organised by Statistics Canada and the United States Census Bureau (April 1–3, 1992), "Ethnicity is a fundamental factor in human life: it is a phenomenon inherent in human experience." However, many social scientists, like anthropologists Fredrik Barth and Eric Wolf, do not consider ethnic identity to be universal. They regard ethnicity as a product of specific kinds of inter-group interactions, rather than an essential quality inherent to human groups.

Processes that result in the emergence of such identification are called ethnogenesis. Members of an ethnic group, on the whole, claim cultural continuities over time. Historians and cultural anthropologists have documented, however, that often many of the values, practices, and norms that imply continuity with the past are of relatively recent invention.

According to Thomas Hylland Eriksen, the study of ethnicity was dominated by two distinct debates until recently. One is between "primordialism" and "instrumentalism". In the primordialist view, the participant perceives ethnic ties collectively, as an externally given, even coercive, social bond. The instrumentalist approach, on the other hand, treats ethnicity primarily as an ad-hoc element of a political strategy, used as a resource for interest groups for achieving secondary goals such as, for instance, an increase in wealth, power or status. This debate is still an important point of reference in Political science, although most scholars' approaches fall between the two poles.

The second debate is between "constructivism" and "essentialism". Constructivists view national and ethnic identities as the product of historical forces, often recent, even when the identities are presented as old. Essentialists view such identities as ontological categories defining social actors, and not the result of social action.

According to Eriksen, these debates have been superseded, especially in anthropology, by scholars' attempts to respond to increasingly politicised forms of self-representation by members of different ethnic groups and nations. This is in the context of debates over multiculturalism in countries, such as the United States and Canada, which have large immigrant populations from many different cultures, and post-colonialism in the Caribbean and South Asia.