Problematic substance use(alcohol, tobacco, and other drugs; ATOD) increases dramatically duringadolescence and emerging adulthood. These problems carry extremely high social,psychological, and economic costs for individuals, families, communities andsociety at large. Although substance use is common among adolescents and youngadults, there are substantial individual differences in susceptibility to substanceuse problems. Why do some adolescents show persistent substance use problemsacross the transition to early adulthood, whereas others show decliningpatterns of use? Currently, there are significant gaps in our understanding ofhow adverse experiences in early childhood may become translated into latersubstance use problems, an issue that has strong relevance for prevention.Using new data from our 17-year prospectivelongitudinal study, we tested the hypothesis that individual differences in theseverity of ATOD among emerging adults may reflect complex transactions betweenchildren’s adverse social experiences and regulatory vulnerabilities that beginin the early preschool years.