Increased sharing of health data among all stakeholders in the health system—from patients and advocates to health professionals and medical researchers—is essential for creating a learning health system. Such a system would leverage health data from a variety of sources to meet the challenges of increasingly complex medical decisions and, in the process, create knowledge more efficiently in the service of producing better patient outcomes and less waste. Government agencies, nongovernment organizations (including charitable foundations and disease advocacy organizations), and the research community have taken important strides in recent years toward greater openness of research data and personal health data. In particular, there is increasing movement toward clarifying people’s rights to their own health data, promoting standards to ease their access, and providing tools that enable them to exercise their rights. Major challenges remain, however, in overcoming the resistance to data-sharing that prevents scientists from learning about clinical trials whose results are unpublished and prevents other people from acquiring and sharing their own health-related data. Those challenges create a need for incentives (financial and otherwise) to create an open-data culture, for changes in laws and regulations to make data-sharing easier, for improvement in the infrastructure used for data-sharing, and for investment in research to increase data-sharing abilities. Policies promoting a more open system should be evaluated to quantify the transition to a data-sharing ecosystem and the opportunities to improve its effectiveness in promoting clinical quality, patient choice, and scientific progress. Given the scale of the challenges and the potential rewards, a strategic federal initiative that aligns current and future efforts would be one way to accelerate movement toward a more open, people-centric health system with data-sharing at its core.