The U.S. health-care sector is large and growing—health-care spending in 2011 amounted to $2.7 trillion and 18 percent of GDP. Approximately half of health-care output is allocated via markets. In this paper, we analyze the industrial organization literature on health-care markets, focusing on the impact of competition on price, quality, and treatment decisions for health-care providers and health insurers. We conclude with a discussion of research opportunities for industrial organization economists, including opportunities created by the U.S. Patient Protection and Affordable Care Act.