Since 1975, the Social Security Administration (SSA) has paid benefits to poor children with disabilities through the Supplemental Security Income (SSI) program. In 2013, approximately 1.3 million children received SSI disability benefits, roughly half of whom qualified primarily due to a mental disorder. In response to considerable and recurring interest in the growth and sustainability of the SSI program for children, SSA commissioned the National Academies of Sciences, Engineering, and Medicine to identify trends in the prevalence of mental disorders among U.S. children and to compare those trends to changes observed in the SSI childhood disability population. The resulting report, Mental Disorders and Disabilities Among Low-Income Children, provides evidence-based findings and conclusions concerning trends in the prevalence of mental disorders in children and also the diagnosis and treatment of these children. This report includes a novel review of previously unreleased data on the rates of mental disorders and disabilities among low-income children from the SSI program and from Medicaid.