This document summarizes a presentation on trends in cohabitation across the Americas from 1970 to 2010. It finds that rates of cohabitation have risen dramatically in all countries and social groups, driven by factors like weakening religious influence, individualism, and a broader ethics revolution. Cohabitation is still increasing and has spread from poorer to richer populations. Contextual factors like education, ethnicity, and country-specific interactions are highly significant. Fertility postponement among educated women may now counterbalance rising teenage births in some settings.