To reduce unnecessary care and improve patient outcomes through bundled payments or population health management, healthcare organizations must define both the population for which they are assuming risk and the services that they will provide. Organizations also must be able to manage variations in cost and quality and demonstrate both the economic and clinical value they provide to the populations they serve. To effectively coordinate care across a patient population, providers--including physicians, hospitals, and postacute care facilities--must be willing to collaborate on efforts to reengineer care delivery.