At the ten year mark since the passage of the Affordable Care Act (ACA), a substantial body of research has investigated the effects of the Medicaid expansion on coverage; access to care and related measures (including utilization, quality of care and health outcomes, provider capacity, and affordability and financial security); and various economic measures. This issue brief summarizes findings from 404 studies (including 80 newly included since the last update of this analysis) of the impact of state Medicaid expansions under the ACA published beginning in January 2014 (when the coverage provisions of the ACA went into effect) and updates earlier versions of this brief with studies through January 2020.