Marriage is one of our most consequential social institutions: it provides a legal and moral scaffolding around which many individuals form deep and enduring personal relations. Civil marriage is socially legible: it provides a way for two people to publicly declare their mutual commitment and enlist social norms and expectations that help stabilize the commitment. Marriage is more flexible and less obligatory than it used to be, but it still shapes family life, intergenerational ties, and social relations broadly. This chapter considers some major marriage controversies, including conservative opposition to same-sex marriage and the complaints of progressive marriage critics. It explains the case for state recognition of monogamy, and considers the charge that marriage unfairly favours particular ethical ideals.