Two of the strongest influences on young adult risk taking decisions are alcohol use and social context. Yet the principal investigator the known potency of each factor in individually inducing risk-taking among youth, and the principal investigator the frequency with which young people consume alcohol in the presence of their peers, no prior research has sought to examine their concurrent and potentially interactive effects. In our model of decision-making in adolescence and young adulthood, asynchronous maturational changes in the brain's cognitive control and reward processing systems yield a period of increased proclivity for risk, and increased susceptibility to specific influences on decision-making. We hypothesize that alcohol and peer influences have their primary impacts on separate components of the brain's decision-making circuitry, with alcohol-affecting regions most closely linked to cognitive control, and peer influence acting upon the reward processing system. The combination of these individually deleterious influences may thus create a powerful risk-taking cocktail that disrupts processing within normally offsetting components of the brain's decision-making circuitry, and thereby increases the tendency to engage in risk-taking behaviors with potentially serious consequences (e.g. reckless driving, risky sexual activity, crime). The present application includes behavioral studies designed to test the main and interactive effects of acute alcohol consumption and peer influence on young adults' decisions about risk, as well as an fMRI studies designed to test our neurobiological framework for adolescent and young adult decision-making and the associated hypothesis regarding the separate neural loci of alcohol and social influences. In order to conduct these studies, a research team with combined expertise in the cognitive neuroscience of executive function, the psychosocial development of adolescents and young adults, and the influences of alcohol on cognition and affect, has been assembled. The proposed studies will yield fundamental insights into the effects of social context and alcohol on young adults' risk-taking behaviors, and will inform the development of more effective prevention and intervention strategies.