The US health care system is in a period of unprecedented change. The threats posed by increasing health care costs and the growing consensus that much of current spending is wasted1 have stimulated a broad array of public and private initiatives aimed at improving care and lowering costs: new technologies, increased investments in patient-centered outcomes research (PCOR), public reporting on the quality and cost of care, pay-for-performance initiatives; and continued efforts to adopt value-based payment models. The health system has responded. For example, the number of accountable care organizations (ACOs) has increased from a handful in 2009 to more than 700 in 2015.2