To achieve the aims of the Affordable Care Act, state and federal regulators must construct an effective system of risk adjustment, one that protects health insurers that attract a disproportionate share of patients with poor health risks. This brief, which summarizes a Commonwealth Fund–supported conference of leading risk adjustment experts, explores the challenges regulators will face, considers the consequences of the law’s risk adjustment provisions, and analyzes the merits of different risk adjustment strategies. Among other recommendations, the brief suggests that regulators use diagnostic rather than only demographic risk measures, that they allow states some but limited flexibility to tailor risk adjustment methods to local circumstances, and that they phase in the use of risk transfer payments to give insurers more time to predict and understand the full effects of risk adjustment.