Abstract Adolescent Brain Cognitive Development (ABCD) is the largest long-term study of brain development and child health in the United States. ABCD consists of a Coordinating Center, a Data Analysis and Informatics Resource Center, and 21 research sites across the U.S. ABCD has enrolled a diverse sample of 11,880 9-10 year-olds, and is tracking their biological and behavioral development through adolescence into young adulthood. All participants receive repeated state-of-the-art neuroimaging, neuropsychological testing, bioassays, and detailed youth and parent assessments of substance use, mental health, physical health, and culture and environment. In March 2020, when our participants were ages 11-13, the world became substantially affected by the COVID- 19 pandemic. ABCD sent surveys to all participating youth and their parent in May, June, August, and October to characterize the impact of the pandemic in their schooling, economics, stress, substance use, routines, and relationships. The proposed project extends the duration of observation through the pandemic and seeks to increase the response rate and representativeness of the survey data. This situational information leverages existing ABCD data to examine pandemic-related perturbations in developmental trajectories of brain functioning, cognition, substance use, academics, social functioning, and physical and mental health. The proposed project will query ABCD participants and their parents about the impact of the pandemic on their lives over the months of school closures, job loss, disease spread, information and misinformation, and, potentially, vaccinations and easing of stressors. This will allow the consortium and scientific community to test hypotheses on how facets of the pandemic affect development. This includes: (1) characterizing the impact of the pandemic on brain and cognitive development and onset of substance use; (2) evaluating the extent to which various schooling approaches exacerbate or mitigate the impact of the pandemic on brain and cognitive development and substance use outcomes; (3) determining the extent to which family stressors exacerbate or mitigate the impact of the pandemic on neurobiological, cognitive, and substance use outcomes; and (4) evaluating short and long-term physical, mental health, neural, and neurocognitive outcomes in youth who personally had COVID-19 illness.