Achieving the triple aims—higher-quality patient-centered care, improving population health, and moderating per capita costs—will require fundamental change in the US health care system.1 Accountable care organizations (ACOs) as outlined in the Affordable Care Act represent an early initiative in restructuring health care.2 Accountable care organizations accept responsibility for the cost and quality of care for defined patient populations. Under the Medicare shared savings program, ACOs will face expenditure targets based on their previous 3 years of Medicare Part A and Part B experience.3 Qualifying organizations can choose between 2 risk arrangements. The first involves upside potential from shared savings in the first 2 years, adding downside risk only in the third year of operation. In the second arrangement, organizations share a greater percentage of the savings but are responsible for downside risk from the beginning. The shared savings program will require organizations to conduct quality improvement initiatives, care coordination, performance measurement, and public reporting.