The spread of accountable care organizations (ACOs) in a multipayer environment faces numerous barriers and requires significant technical work. In phase 1 of this project, the investigative team developed a 'starter set' of health care claims-based measures that could be used to assess quality of care as well as determine payments to ACO providers and the shared savings for which they are eligible. In phase 2, the team will develop and test a more advanced set of measures with pilot sites, including clinical outcomes measures and patient-reported measures of care experience and health status. A framework for evaluating the implementation and sustainability of new ACOs will also be created. This work will be of great interest to the Centers for Medicare and Medicaid Services (CMS) and other organizations as they prepare for nationwide implementation of the ACO model.