The Adolescent Brain Cognitive Development Study (ABCD) will capture a breadth of multi-faceted biobehavioral, environmental, familial, and genetic longitudinal developmental open-access data from over 11,000 9–10 year olds throughout the United States of America (USA) for an envisioned ten-year span. This will subsequently represent the largest study ever attempted with this level of brain phenotypic detail. This study holds the opportunity for exciting advances in the understanding of typical adolescent neurodevelopment, discovery of neurodevelopmental underpinnings of mental illness, as well as the neurodevelopmental influences of (and on) social factors, substance use, and critically – their interaction. This project will certainly take unprecedented steps in informing the nature of adolescence and the developing brain. The scale and open-access features of ABCD also necessarily entail areas for consideration to enhance the integrity of the ABCD study, and protect against potential misuse and misinterpretation of ABCD data. Ultimately, with the open-source data, all scientists in the broader community have as much responsibility as the investigators within the Consortium to treat these data with care. It will be fascinating to see what dynamic data these paths generate. ABCD is poised to exemplify how large-scale longitudinal developmental neuroscientific studies can be designed and efficiently conducted.