The U.S. spends about 18% of its gross domestic product on health care, far more than most countries. One contributing factor that often goes overlooked: the high cost, in time and money, of becoming a physician. In a recent paper for the Mercatus Center, Jeffrey Flier and Jared Rhoads argue that the amount of time it takes to become a doctor—almost always at least a decade—constrains the supply, driving up prices. Physician incomes in the U.S. well exceed those in Europe; American generalists earn twice as much as Dutch ones.