Educational assortative mating refers to the tendency of individuals to choose partners with similar levels of educational attainment. The reversal in the gender education gap, as women become more educated than men, has increased the rate of couples where both partners are college graduates and decreased the rate of couples where the woman is less educated than her husband. In contrast, the rate of couples where the woman is more educated than her husband increased substantially. These trends in assortative mating are observed in most developed countries worldwide. Trends in marriage by education level affect household income, household consumption, and women’s bargaining power. Increasing assortative mating may lead to greater inequality and lower intergenerational social mobility. However, there is debate in the literature on how educational assortative mating should be measured, whether it has increased, and the extent to which it may have contributed to the rise in inequality. This chapter reviews the evidence on educational assortative mating, its effects on socioeconomic behavior, and its contribution to inequality.