Marriage regulations are the culturally defined rules and norms that govern who can marry whom within a society. These regulations are crucial for maintaining social order, defining kinship structures, and perpetuating cultural values. They typically include rules of endogamy, which dictate marriage within a specific social group (e.g., caste, religion, ethnic group), and exogamy, which requires marriage outside a particular group (e.g., clan, lineage, village). Additionally, societies often have rules regarding preferred marriage partners (e.g., cross-cousin marriage) or prohibited unions (e.g., incest taboos, parallel-cousin marriage in some cultures). These rules serve various functions, such as preventing genetic inbreeding, consolidating wealth and power, strengthening social ties, and defining an individual's social status and obligations.

Alliance Theory, primarily associated with French anthropologist Claude Lévi-Strauss, offers a structuralist perspective on marriage. It posits that marriage is not merely an individual union but fundamentally a mechanism for establishing alliances between different social groups, such as families, clans, or lineages. Lévi-Strauss argued that the universal incest taboo, by prohibiting marriage within the immediate family, compels individuals to seek partners outside their kin group, thereby initiating a system of exchange. This exchange, particularly the exchange of women, creates reciprocal obligations and solidarity between groups, forming complex networks of alliances that structure society. The theory emphasizes that these alliances are crucial for social cohesion, economic cooperation, and political stability, transforming potentially isolated kin groups into an interconnected social fabric. Alliance theory contrasts with descent theory, which focuses on how individuals trace their ancestry and group membership.

In essence, marriage regulations are the practical, observable rules that societies implement, while alliance theory provides a theoretical framework for understanding the deeper social functions and structural implications of these rules. The specific patterns of endogamy and exogamy, and the preferences for certain types of partners, are all manifestations of the underlying principles of alliance formation, demonstrating how marriage serves to create and maintain social bonds beyond the immediate conjugal unit.