Project Summary Childhood temperament broadly shapes psychological adjustment across the lifespan, having particular influence during critical and complex periods of development such as adolescence. While risk for psychopathology rises sharply during adolescence, temperamental differences further enhance risk. Behavioral Inhibition (BI) is a temperament identified early in life, marked by strong physiological, behavioral, and emotional reactions to unfamiliar contexts, and associated with a four-fold increased risk for anxiety disorders in mid-adolescence, as well as mood disorders and substance abuse in late adolescence. Despite the dramatic increase in risk, we have found that not all children with a childhood history of BI go on to display psychopathology. Given this heterogeneity in risk outcomes, it is critical to identify the mechanisms that differentiate adolescents who struggle from those who adapt despite early risk factors. For adolescents with a history of BI, the increasing demands of their rapidly evolving social context may be particularly challenging. Unsuccessful attempts to negotiate the complex social challenges of adolescence are linked to increases in psychopathology, making mid-adolescence a critical period for isolating mechanisms that might influence variability in outcomes. We are proposing to examine two such mechanisms, cognitive control and supportive relationships with friends and parents, and their impact on adolescents’ reactions to, and regulation following, social challenges assessed in the laboratory and using daily diary reports. We will examine: (1) two types of cognitive control (reactive versus proactive) with the expectation that reactive control will be positively associated, and proactive control will be negatively associated with heightened reactions to social challenge and greater psychopathology, and (2) the effects of supportive relationships with friends and parents with the expectation that such relationships will buffer the effects of stressful social challenges and increased incidence of psychopathology. Finally, we will examine whether adolescents’ responses to social challenge mediate the association between childhood history of BI and psychopathology in late adolescence.