Are hospitals or physicians more responsible for driving up the price of hospital-based care? Tracking provider spending growth — and identifying the underlying forces at play — is an important issue for policymakers. Using data on actual prices paid by health insurers, Commonwealth Fund–supported researchers analyzed hospital and physician prices for inpatient and hospital-based outpatient services as well as for four high-volume services: cesarean section, vaginal delivery, hospital-based outpatient colonoscopy, and knee replacement. The study, published in Health Affairs, offers an analysis of price trends that can guide future cost-containment efforts.