Improving medication adherence has been identified as a crucial step towards improving health outcomes for patients with chronic disease and has provided the motivation for many changes in our health care system. Despite the volume of research done on this topic, however, we still lack important basic information about how to improve adherence in a cost-effective way. There is a need for a better understanding of what areas of research are most likely to produce advances that could be used by policymakers, providers, payers, or other stakeholders to generate real improvements in medication adherence. To address this, we developed a set of research priorities designed to improve understanding about whom to target for adherence interventions and which particular interventions to employ for specific subpopulations. To produce this research agenda, we synthesized information from the existing literature with a series of stakeholder interviews and expert panel meetings. We identified 6 key areas for research: (1) predicting nonadherence, (2) behavioral factors affecting nonadherence, (3) measuring the impact of nonadherence on health and cost outcomes, (4) effectiveness of existing interventions, (5) misaligned incentives between payers and providers, and (6) provider training and coordination of care. We provide detailed descriptions and example topics within each area. As the health care system continues to embrace reforms designed to improve the value of care, more and better information is needed to guide efforts designed to improve medication adherence. Addressing the topic areas identified here will be an important step towards accomplishing this goal.