In the new issue of Health Affairs, Carrie H. Colla of the Dartmouth Institute for Health Policy and Clinical Practice and colleagues report findings from a survey of accountable care organizations (ACOs) across the nation—the first of its kind. According to the Commonwealth Fund–supported survey, just over half of ACOs are physician-led, while another third are jointly led by physicians and hospitals. While physician-led ACOs may face challenges in managing care across settings, their greater focus on outpatient care compared with hospital-led ACOs may allow them to achieve sharper reductions in the use of costly inpatient or postacute care.