The explosive expansion of non-marital cohabitation in Latin America since the 1970s has led to the narrowing of the gap in educational homogamy between married and cohabiting couples (what we call “homogamy gap”) as shown by our analysis of 29 census samples encompassing eight countries: Argentina, Brazil, Chile, Colombia, Costa Rica, Ecuador, Mexico and Panama (N = 2,295,160 young couples). Most research on the homogamy gap is limited to a single decade and a small group of developed countries (the United States, Canada, and Europe). We take a historical and cross-national perspective and expand the research to a range of developing countries, where since early colonial times traditional forms of cohabitation among the poor, uneducated sectors of society have coexisted with marriage, although to widely varying degrees from country to country. In recent decades, cohabitation is emerging in all sectors of society. We find that among married couples educational homogamy continues to be higher than for those who cohabit, but in recent decades the difference has narrowed substantially in all countries. We argue that assortative mating between cohabiting and married couples tend to be similar when the contexts in which they are formed are also increasingly similar.