The Affordable Care Act expands Medicaid in 2014 to millions of low-income adults in states that choose to participate in the expansion. Since 2010 California, Connecticut, Minnesota, and Washington, D.C., have expanded coverage earlier to a portion of low-income childless adults. Using administrative records, the authors document that the ramp-up of enrollment was gradual over time in California, Connecticut, and D.C. Survey data on the two earliest expansions show strong evidence of increased Medicaid coverage in Connecticut and positive but weaker evidence of increased coverage in D.C. Medicaid enrollment rates were highest among people with health-related limitations. In Connecticut, evidence of some crowd-out of private coverage as well as a positive spillover effect on Medicaid enrollment among previously eligible parents was found.