Ever since the Centers for Medicare & Medicaid Services (CMS) released the Accountable Care Organization (ACO) final rule in October 2011, the American Society of Nephrology (ASN) has been analyzing the rule to determine how it may affect patients with kidney disease and the nephrologists who care for them. In the second of a series of Q & A articles with members of the ASN ACO Task Force, Amy Williams, MD, Dan Weiner, MD, and Emily Robinson, MD, answer questions about who can join ACOs and about other new care delivery models.