Background: Mexico experienced a boom in cohabitation during the 2000s, which has sparked a debate about whether the nature of cohabitation has changed along with its increasing overall rates and diffusion to diverse social groups.

Objective: We examine continuity and change in the dynamics of cohabitation in Mexico to address whether it has largely hewed to prior patterns or taken on new forms.

Methods: We analyze the marital histories of 99,387 female respondents in the 2009 National Survey of Demographic Dynamics using multistate event-history techniques.

Results: Mexico's cohabitation boom of the 2000s was driven by cohorts born after 1975, whose cohabiting unions are less likely to transition to marriage than those formed by earlier cohorts. However, the tendency of cohabiters to marry is greater among the higher educated.

Conclusions: Cohabitation in Mexico used to be rare, concentrated among less-educated women, and mostly a prelude to marriage. As it became more common in the 2000s it also took on at least two distinct patterns. Among the less educated, cohabitation became a common union-formation option, shifting to a longer-term substitute for marriage. Cohabitation also grew, from a lower baseline, among the upper educated; but for them, it is usually a short stage, either transitioning to marriage or ending in separation.

Contribution: Our findings contribute to the literature on international family change by providing an additional case study, different in geographical and cultural setting, of the global rise of cohabitation.