As part of their contracts with providers working in accountable care organizations (ACOs), public and private payers offer incentives to keep down costs and improve the quality of care that patients receive. A Commonwealth Fund–supported study finds that these incentives can have positive spillover effects for patients not specifically targeted by the incentives—in this case, significantly lower spending on outpatient care. The findings suggest that providers’ responses to the ACO initiative led to broad changes in patient care.