The authors examine the prevalence in the United States of childhood disability and of the conditions responsible for impairment, as well as trends in the prevalence of chronic conditions associated with disability. They find that childhood disability is increasing and that emotional, behavioral, and neurological disabilities are now more prevalent than physical impairments. They stress the importance of, and lack of progress in, improving socioeconomic disparities in disability prevalence, as well as the need for better measures and greater harmonization of data and data sources across different child-serving agencies and levels of government. They call on policy makers to strengthen existing data systems to advance understanding of the causes of childhood disabilities and guide the formulation of more strategic, responsive, and effective policies, programs, and interventions.