This literature review summarizes findings from 404 studies of the impact of state Medicaid expansions under the ACA published between January 2014 (when the coverage provisions of the ACA went into effect) and January 2020. It includes studies, analyses, and reports published by government, research, and policy organizations using data from 2014 or later. This body of research suggests that the expansion presents an opportunity for gains in coverage, improvements in access and financial security, and economic benefits for states and providers.