This chapter reviews models of marriage, with special emphasis on how the sex ratio can help explain outcomes such as marriage formation, the intramarriage distribution of consumption goods, labor supply, savings, type of relationship, divorce, and intermarriage. Economic models of marriage pioneered by Gary Becker are reviewed in the first section and then extended in the next section to incorporate the labor market for the work-in-household approach of Grossbard. The following section discusses challenges in identifying exogenous variation in sex ratios and presents empirical evidence on the impact of sex ratios on labor supply, consumption, savings, and several other outcomes.