Recent health care payment reforms aim to improve the alignment of Medicare payment strategies with goals to improve the quality of care provided, patient experiences with health care, and health outcomes, while also controlling costs. These efforts move Medicare away from the volume-based payment of traditional fee-for-service models and toward value-based purchasing, in which cost control is an explicit goal in addition to clinical and quality goals. Specific payment strategies include pay-for-performance and other quality incentive programs that tie financial rewards and sanctions to the quality and efficiency of care provided and accountable care organizations in which health care providers are held accountable for both the quality and cost of the care they deliver.Accounting for Social Risk Factors in Medicare Payment: Identifying Social Risk Factors is the first in a series of five reports commissioned to provide input into whether socioeconomic status (SES) and other social risk factors could be accounted for in Medicare payment and quality programs. This report focuses on defining SES and other social factors for the purposes of application to Medicare quality measurement and payment programs.