Who is your mother's brother's daughter? In some societies, she is your sister. In others, she is your cousin. Kinship is the system of social relationships based on descent and marriage. It defines who is related to whom, what obligations they have, and how property and status pass between generations.

Anthropologists and sociologists study kinship because it organizes so much of social life. In small-scale societies, kinship determines residence, inheritance, political alliances, and religious roles. In modern societies, kinship still matters, though it shares space with other institutions.

Key concepts

• Descent: matrilineal, patrilineal, or bilateral
• Marriage: exogamy (outside group) or endogamy (inside group)
• Kinship terms: mother, father, aunt, uncle, cousin
• Fictive kinship: close non-blood relationships treated as family

Kinship systems are not fixed. They change with migration, technology, and law. Same-sex marriage, adoption, and assisted reproduction have expanded what counts as kin. Godparents, close friends, and chosen families blur the line between blood and bond.