SUMMARY The goal of this proposed project is to determine how social environments in schools and communities generate ? or ameliorate ? vulnerability to youth suicide and suicide clusters (S/SC) through cultural, organizational, and social-ecological pathways. In the context of rising rates of youth S/SC and diminishing school resources, understanding schools as both a possible source of vulnerability and as a key place for suicide pre- and postvention (SPP) is increasingly critical. Research suggests that the social environment matters to youth S/SC; yet to date studies have neglected to examine how variation in schools? cultural systems and mental health safety systems, as well as their broader social-ecological contexts ? including access to resources and bridges between schools and healthcare ? explain variation in S/SC between schools. Further, research fails to consider how schools, as formal organizations, work on a daily basis to prevent suicide while navigating competing responsibilities often under conditions of resource scarcity. Understanding the root environmental causes of S/SC and identifying effective and sustainable strategies for schools SPP requires addressing these gaps. The specific aims guiding the proposed project are (Aim 1) to identify characteristics of schools? cultural systems that facilitate youth well-being; (Aim 2) to determine the organizational elements that enable schools to create mental health safety systems that effectively identify, triage, and support vulnerable youth; and (Aim 3) to assess the components of broader social-ecological systems that serve as barriers or enablers of schools? strategies to support youth well-being and prevent S/SC. To accomplish our aims, we employ a mixed-method, comparative research design and rely on an established partnership with two Colorado public school districts and their 10 heterogeneous high schools (3 of which have serious, enduring youth S/SC problems). We have unprecedented access to observe how schools work on a daily basis to prevent suicide and support MH. Further, we integrate observational data with interviews and surveys with members of the school ? specifically, youth, parents, school-based police officers, and other school staff ? and broader communities ? especially, healthcare workers, therapists, crisis responders, and religious leaders ? to identify challenges to and enablers of schools? SPP strategies. This project is led by a new investigator with a strong record of research on youth S/SC who is supported by an established interdisciplinary team with extensive methodological and topic expertise. Preliminary fieldwork produced the strong collaborative relationships ? with the districts, schools, and community leaders as well as the members of the youth, community, and academic advisory boards ? necessary for the successful completion of the project?s aims and for advancing scientific frameworks for developing and deploying sustainable, equitable, and effective SPP in schools and communities to reduce youth suicide and improve population health.