The Adolescent Brain Cognitive DevelopmentSM (ABCD) Study is the largest longitudinal study of brain development and child health in the U.S., collecting data from more than 11,000 children across the country beginning when they were 9-10 years old and continuing for a decade. In addition to behavioral assessments, youth undergo neuroimaging and provide biospecimens, including oral fluids for hormone analysis, urine and hair for substance use and exposure, deciduous teeth for environmental exposures, and blood for genetic analysis and metabolic and hematologic assays. This initiative allows investigators to apply for access to biological samples from the ABCD Study .