Although policymakers are increasingly interested in how integrated delivery systems and managed care plans implement clinical guidelines and improve performance and quality of care, few data have been compiled about how these organizations are undertaking change. Interviews with officials in organizations that are engaged in improving practice across the country documented that there is a profound transformation under way with substantial similarity in the approaches being used by otherwise very different plans. Better evaluation of the effectiveness and cost-effectiveness of these approaches could provide a more solid foundation for policies to improve quality of care.