By 2014, each of the fifty states and the District of Columbia will have a new health insurance exchange, or marketplace, established under the Patient Protection and Affordable Care Act. These exchanges are the centerpiece of the reform law: they will be the main portals where people who do not have health insurance coverage through their jobs and small businesses will go, either in person or online, to find a health plan and to learn about and apply for federal subsidies. The most immediate challenge facing all fifty-one exchanges is fulfilling their most basic role: ensuring that all who are eligible to enroll in qualified health plans and to receive federal subsidies in fact enroll.