Using data from the nationally representative 2010 Married and Cohabiting Couples Survey of different-sex cohabiting and married couples, we compared the relationship quality of today’s cohabitors and marrieds. Consistent with diffusion theory and recent conceptual work on the deinstitutionalization of marriage, we found that the relationship between union type and relationship quality is now bifurcated with direct marrieds reporting the highest relationship quality and cohabitors without marriage plans reporting the lowest marital quality. In the middle were the two largest groups: marrieds who premaritally cohabited and cohabitors with plans to marry. These two groups did not differ in terms of relationship quality. This study adds to the growing literature indicating that the role of cohabitation in the family life course is changing in the contemporary context.