A family consists of a domestic group of people (or a number of domestic groups), typically affiliated by birth or marriage, or by comparable legal relationships — including domestic partnership, adoption, surname and (in some cases) ownership (as occurred in the Roman Empire).

Although many people (including social scientists) have understood familial relationships in terms of "blood", many anthropologists have argued that one must understand the notion of "blood" metaphorically, and that many societies understand 'family' through other concepts rather than through genetics.