We use data from Denmark, Germany, Norway, the United Kingdom, and the United States to document the degree of educational assortative mating, how it evolves over time, and the extent to which it differs between countries. This descriptive analysis motivates and guides a decomposition analysis in which we quantify the contribution of various factors to the distribution of household income. We find that assortative mating accounts for a nonnegligible part of the cross-sectional inequality in household income in each country. However, changes in assortative mating over time barely move the time trends in household income inequality.