California has long been a leader in expanding the eligibility criteria for enrollment in Medicaid. Under the Affordable Care Act (ACA), states can expand Medicaid to cover more adults with low incomes, and California was among the first to do so with its program, Medi-Cal. To date, 36 states and the District of Columbia have adopted the expansion, and newly released research suggests residents in those places are experiencing tangible improvements in their health and well-being as a result.