Project Summary Elucidating the impact of socio-economic status (SES) and environmental factors on cognitive and brain development is critical for understanding the pathways to substance abuse during adolescence. Previous studies suggest that low SES can negatively impact cognitive functioning as well as brain maturation. This proposal aims to examine the impact of SES on cognitive function and brain development in the current ABCD study data release of ~4500 children, ages 9 and 10 years of age. Further, environmental factors of tobacco smoke exposure and bilingualism will be examined. These environmental factors often co-occur with low SES demographics and examining their contributions to cognitive function and brain development may inform the extent to which cognitive function and the brain is impacted by environmental factors during childhood. The ABCD study dataset has many notable strengths, including the availability of various cognitive and brain imaging measures, and a large sample size. In addition, the narrow age range, makes it less likely that differences in cognitive function and brain development will be due to differences in generations between children in wider age groups. The analyses proposed in this supplement will capitalize on the strengths of the ABCD sample to test hypotheses that will inform the relationship between environment, cognition, and the brain. Findings from this proposal will form the basis for future analyses that examine the relationships between substance use and cognitive function and brain development during adolescence, as well as understanding the contribution of environmental factors to such relationships.