The Affordable Care Act (ACA) led to historic gains in health insurance coverage by extending Medicaid coverage to many low-income individuals and providing Marketplace subsidies for individuals below 400% of poverty. The number of uninsured nonelderly Americans decreased from over 44 million in 2013 (the year before the major coverage provisions went into effect) to just below 27 million in 2016. However, in 2017, the number of uninsured people increased by nearly 700,000 people, the first increase since implementation of the ACA. Ongoing efforts to alter the ACA or to make receipt of Medicaid contingent on work may further erode coverage gains seen under the ACA. This fact sheet describes how coverage has changed in recent years, examines the characteristics of the uninsured population, and summarizes the access and financial implications of not having coverage.