Chloe Bird and Patricia Rieker argue that to improve men's and women's health, individuals, researchers, and policymakers must understand the social and biological sources of the perplexing gender differences in illness and longevity. Although individuals are increasingly aware of what they should do to improve health, competing demands for time, money, and attention discourage or prevent healthy behavior. Drawing on research and cross-national examples of family, work, community, and government policies, the authors develop a model of constrained choice that addresses how decisions and actions at each of these levels shape men's and women's health-related opportunities. Understanding the cumulative impact of their choices can inform individuals at each of these levels how to better integrate health implications into their everyday decisions and actions. Their platform for prevention calls for a radical reorientation of health science and policy to help individuals pursue health and to lower the barriers that may discourage that pursuit.