Health care systems are under pressure to control their increasing costs, to better adapt to evolving demands, to improve the quality and safety of care, and ultimately to ameliorate the health of their populations. This article looks at a battery of organizational options aimed at transforming health care systems and argues that more attention must be paid to reforming the delivery mechanisms that are so crucial for health care systems' overall performance. To support improvement, policies can rely on organizational assets in two ways. First, reforms can promote the creation of new organizational forms; second, they can employ organizational levers (e.g., capacity development, team-based organizations, evidence-informed practices) to achieve specific policy goals. In both cases organizational assets are mobilized with a view to creating complete health care organizations — that is to say, organizations that have the capacity to function as high-performing systems. The challenges confronting the development of more complete health care organizations are significant. Real health care system reforms may likewise require implementing ecologies of complex innovation at the clinical, organizational, and policy levels. Policies play a determining role in shaping these new spaces for action so that day-to-day practices may change.