The 2014 Listening Project Report identified several research and data gaps related to Medicare. Among these was a need for research regarding Medicare accountable care organizations’ (ACOs) effect on the health care marketplace, including ACO impact on competition,cost, quality and access to care. This Roadmap focuses on these issues. A separate Roadmap examines evidence relevant to understanding the internal structure and operation of Medicare ACOs. The Roadmaps were produced with the support of the Robert Wood Johnson Foundation.