A single marketplace facilitating the buying and selling of private health insurance. The Affordable Care Act (ACA) called for the creation in every state of exchanges through which individuals who are U.S. citizens or legal residents, and businesses, can buy coverage. At the end of 2016, 23 states including the District of Columbia were running their own marketplace or had built one in partnership with the federal government. The remaining states are using the healthcare.gov marketplace, which is run by the federal government.