Under the Affordable Care Act, Medicare will launch a Shared Savings Program for groups of health care providers that join forces, with or without hospitals or health plans, to form legal entities that agree to take responsibility for the quality, cost, and overall care of a population of patients. What will these accountable care organizations (ACOs) look like? Who will step forward to form them? What are the best pathways and likely hurdles to achieving ACO status? What are the risks of entering the arena, and what are the expected benefits for clinicians and patients? In a roundtable discussion moderated by Dr. Thomas Lee, experts Lawrence Casalino, Elliott Fisher, and Gail Wilensky explored these and other questions.