PROJECT SUMMARY/ABSTRACT Millions of children in the United States are living in high-poverty neighborhoods, where they are at risk for exposure to higher rates of crime, violence and neighborhood-level disorder than peers living in more affluent neighborhoods (Friedson & Sharkey, 2015). These disadvantageous neighborhood conditions predict depression, anxiety and conduct disorder in adolescents (Aneshensel & Sucoff, 1996), but it is unclear exactly how neighborhood disadvantage confers risk for these mental health outcomes. Cortisol reactivity to acute stress is a candidate mechanism, given that cortisol reactivity is thought to be a link between adverse experiences and psychopathology (Koss & Gunnar, 2018). However, little is known about the degree to which neighborhood disadvantage influences adolescent cortisol reactivity. The proposed study has 3 aims: 1) examine the association between neighborhood disadvantage and cortisol reactivity; 2) identify potential moderators of this association; and 3) investigate cortisol reactivity as a mediator of the association between neighborhood disadvantage and adolescent mental health. At age 13, neighborhood-level disadvantage (i.e., dangerousness, physical decay and disorder) will be coded using a novel social observation protocol, the Systematic Social Observation Inventory-Tallying Observations in Urban Regions (SSO i-Tour). Adolescents will also complete the Trier Social Stress Test for Children (TSST-C), a social-evaluative task that reliably evokes a cortisol response (Buske-Kirschbaum et al., 1997). Saliva samples will be collected during the TSST- C and assayed for cortisol concentration. Adolescents will also report on the quality of their relationship with their parent using the Inventory of Parent and Peer Attachment-Revised (IPPA-R, Gullone & Robinson, 2005). At age 14, parents will report on adolescent mental health symptoms using the Child Behavior Checklist (CBCL; Achenbach & Rescorla, 2001). Multivariate regression analysis will be used to examine the association between neighborhood disadvantage and cortisol reactivity, as well as explore moderators (i.e., adolescent sex and relationship quality) of this association. Last, mediation analysis will be employed to examine whether cortisol reactivity mediates the association between neighborhood disadvantage and mental health symptoms. This study aligns with NICHD research priorities due to the examination environmental factors that impact youth stress reactivity and psychosocial adjustment in high-risk contexts. Findings stand to inform the development of interventions to prevent and ameliorate the effects of neighborhood disadvantage on youth mental health by identifying factors that can serve as novel treatment targets. In conjunction with the proposed training plan, this project will provide the applicant with mentorship and training from experts in the fields of neighborhood research, statistics, adolescent development and cortisol reg...