This study explored how health, wealth, and family ties shape older cohabitors' chances of marrying or separating. Drawing on rational choice and exchange theories, the author argues these factors affect women and men differently because the rewards, alternatives, and barriers of later-life union formation differ by gender. The study used panel data from the 1998–2006 Health and Retirement Study and a sample of cohabitors 50 and older (N = 1,136). For older female cohabitors, large families and entitlement income lower the risk of marrying, whereas close social networks raise the risk of separating. Moreover, health and wealth have an interactive relationship in that the risk of marrying is highest for unhealthy male cohabitors when they are very wealthy but is highest for the poorest female cohabitors when they are in excellent health. Older men may be exchanging economic resources for caregiving, and cohabitation may be an adaptive response to the gendered costs and barriers of later-life union formation.