Endogamy is the rule that marriage must take place within a specific social group. The group might be a caste, a religious community, a social class, or a linguistic population. The rule does not mean everyone marries a close relative. It means the pool of acceptable partners is bounded. India's caste system is a well-known example, but endogamy appears in many societies, from European royalty to religious minorities in the Middle East.

Endogamy preserves boundaries. It keeps property, status, and ritual knowledge within a defined group. It can also concentrate genetic disorders, which is why medical researchers study endogamous populations closely. The rule is often reinforced by custom, religious law, and family pressure. Breaking it can bring sanctions ranging from gossip to ostracism.

Common forms

• Caste endogamy, as in parts of South Asia.
• Religious endogamy among minority faiths.
• Class endogamy among elites or landed families.
• Local endogamy, marrying within a village or region.

Endogamy is the mirror image of exogamy. Most societies combine both, requiring marriage outside the family but inside the group.