Patient engagement is an increasingly important component of strategies to reform health care. In this article we review the available evidence of the contribution that patient activation-the skills and confidence that equip patients to become actively engaged in their health care-makes to health outcomes, costs, and patient experience. There is a growing body of evidence showing that patients who are more activated have better health outcomes and care experiences, but there is limited evidence to date about the impact on costs. Emerging evidence indicates that interventions that tailor support to the individual's level of activation, and that build skills and confidence, are effective in increasing patient activation. Furthermore, patients who start at the lowest activation levels tend to increase the most. We conclude that policies and interventions aimed at strengthening patients' role in managing their health care can contribute to improved outcomes and that patient activation can-and should-be measured as an intermediate outcome of care that is linked to improved outcomes.