Incentives under the Affordable Care Act (ACA) are spurring increasing numbers of health care systems to assume the risk of paying for patient care, blurring the boundaries between care delivery organizations and insurers. New arrangements such as bundled payments, value-based purchasing, and accountable care organizations (ACOs) transfer financial risk from payers to health care systems. The union of payer and care delivery functions may engender opportunities for health systems to invest in prevention and more comprehensive, coordinated, patient-centered care.