Many theories based on Darwinian evolutionary theory are of particular relevance to family research. The theory of kin selection is not limited to social behavior of animals, but also explains why humans in all cultures and epochs organize their reproductive and productive activities in family networks and family households. Even though the willingness to cooperate in the human family ultimately goes back to kin selection, it is not the only factor determining the relationships of family members. Genuine altruism between closely related family members is possible due to indirect fitness benefits. However, family members are not only trusting allies, but also fierce competitors. Even among siblings or between parents and children, support and help are not granted unconditionally, but are offered based on a cost-benefit calculation. The costs and benefits depend on the social context. The social context is relevant between societies, for research comparing families across cultures and periods, and for research studying differences within populations between social groups. Inter-societal perspective, which compares the family across cultures and epochs, as well as to Evolutionary family research is therefore fundamentally an interdisciplinary research project. This article introduces the basics of evolutionary family research and illuminates its most important aspects.