An organized delivery system is a network of organizations that provides or arranges to provide a coordinated continuum of services to a defined population and is willing to be held clinically and fiscally accountable for the outcomes and the health status of the population served. As such, organized delivery systems are at the center of efforts to implement health care reform. Based on analysis of 12 such systems, this article identifies key characteristics that influence what organized delivery systems are able to do, outlines the major obstacles or challenges to achieving greater levels of integration, and then discusses a number of approaches for effectively dealing with these obstacles.