Temperament refers to stable individual differences in reactivity observed in infancy that are foundations for later personality. Behavioral inhibition is one such temperament characterized by infants’ overly cautious, fearful, and avoidant responses to unfamiliar people, objects, and situations. This enduring trait shows moderate stability across toddlerhood to middle childhood and is known to influence childhood social and emotional functioning. Inhibited children show difficulties in peer interactions, express social withdrawal, and are at a 4- to 6-fold increased risk for developing anxiety disorders, particularly social anxiety, though only an estimated 40% will develop these disorders. These findings foreshadow difficulties related to psychosocial outcomes in adulthood, a period with new challenges in achieving financial independence, vocational goals, and maintaining multiple social relationships. Yet, little is known about the life-course sequalae of children who began life with an inhibited temperament because longer-term longitudinal studies are rare and costly. We conducted a prospective longitudinal study following a cohort of infants (N=165) across three decades to examine life course outcomes linked to behavioral inhibition observed in infancy. In the year 2018, we collected data on personality, mental health, and sociodemographics from the participants at age 26 (n=109). The current study has two goals: (1) to determine the association between infant BI and reserved adult personality, social functioning, psychopathology, and education/ vocational outcomes in adulthood; and (2) to examine whether the Error Related Negativity measured in adolescence moderated the association between infant BI and psychopathology factors in adulthood. We aimed to use data analytic strategies, structural equation modeling, that are designed to handle large number of variable measuring different aspects of the same constructs. For example, we measure latent constructs of social functioning using multiple scales, including interpersonal competence, social withdrawal, functioning with friends and family and more. Similarly, to examine the relation between infant behavioral inhibition and adult psychopathology, we use structural equation modeling to examine general, externalizing and internalizing psychopathology factors using multiple scales. After defining these constructs and making sure they are valid, we would regress these latent variables onto the predictor variable, infant BI, as well as control variables, such as age at assessment and sex.