Project Summary Trauma-exposed adolescents are at risk for a host of deleterious outcomes, particularly stress sensitive disorders such as acute stress disorder (ASD), posttraumatic stress disorder (PTSD), depression, anxiety, and substance use disorders. Theory and available evidence point to two particularly important influences on the development of PTSD: (1) individual stress response (particularly heart rate (HR), skin conductance (SC)) and (2) social context (interactions occurring in person and through online social networking (OSN)). Whereas prior studies broadly point to self reported social context or single measurements of biomarkers, the present investigation uses naturalistic ecological sampling approaches that permit more objective coding of social behaviors and context and uses continuous biometrical sampling to permit the modeling of coupled individual stress responses and social context. The present investigation, translational in implications for intervention, will longitudinally model the course of early interplay of biomarkers and social context influencing symptom development in 200 trauma-exposed adolescents (13-17 years). Youth will be recruited in-hospital immediately after medical evaluation for traumatic injury (i.e., physical assault, serious vehicular accident) sufficiently life threatening to warrant trauma team activation. They will be asked to wear: (i) a wristband health tracker, for two weeks; (ii) the EAR, for two weeks (later coded for social environment, interaction, affect, content). At 2- week follow-up, youth will: (i) permit download of OSN from 2-weeks pre-trauma through the 2-week follow-up; (ii) participate in a semi-structured clinical interview to assess symptoms of stress-sensitive disorders, and (iii) complete laboratory procedures developed to characterize social and biological processes critical to stress- sensitive disorders. At 6-weeks, 6-months, and 9-months post-trauma, youth will download OSN occurring in the 2 weeks prior as well as complete (i) laboratory procedures, (ii) semi-structured diagnostic interviews of stress-sensitive disorders and (iii) self-report measures of social context. The present investigation will provide rich, clinically relevant characterization of the inter- and intra-individual predictors and correlates of post-trauma adjustment.