Project Abstract Firearm-related injury remains a leading cause of death among adolescents and young adults in the United States. Firearm-related injury mortality rates are remarkably similar in rural communities and urban settings. Handgun carrying is widely recognized as a key risk factor for firearm-related injury, violence, and crime among adolescents in urban settings. It is not clear if these findings generalize to rural communities. A sizable number of firearm-related homicides, suicides, and nonfatal crimes among adolescents in rural communities involve handguns; however, our knowledge of the culture, scope, and developmental patterns of handgun carrying in this population is strikingly limited. Identifying the antecedents and consequences of handgun carrying and developing culturally-appropriate and community-specific interventions that promote prosocial behavior while respecting the distinct rural firearm culture may translate to a lower burden of firearm-related injury among adolescents in rural communities. We propose a project in response to “Research Grants to Prevent Firearm-Related Violence and Injuries (R01)” to improve our understanding of handgun carrying among adolescents in rural communities and provide a strong foundation for effective interventions that prevent firearm-related injury and promote safety in this population. In this project, we will address both Research Objective One and Research Objective Two using Funding Option B indicated on the Notice of Funding Opportunity. We will collect new data on handgun carrying by conducting focus groups among adolescents aged 14-17 currently living in rural communities in Washington State and use existing data on handgun carrying among a gender-balanced and diverse panel of 4,407 youth aged 12 years in 2005 living in 24 communities that participated in a 7-state randomized community trial of the Communities That Care prevention system driven by the Social Development Model. The panel has been followed across 10 waves of data collection through age 26 in 2019. We will also collect new data related to handguns in the next wave of this longitudinal study in 2021 when the sample is, on average, 28 years old. In this project, we will improve our understanding of the cultural and environmental context within which handgun carrying occurs (Aim 1), identify developmental patterns of this behavior among youth in rural communities during adolescence and as they transition to adulthood (Aim 2), examine the salient antecedents and consequences of this behavior (Aim 3), and test the effect of a prevention system on its patterns (Aim 4). Qualitative methods (e.g., thematic coding and qualitative comparative analysis) and quantitative methods (e.g., latent growth mixture modeling and multi- level mixed effects modeling) will be used to address these aims. Rural communities have high levels of firearm access and mortality, yet they are understudied and underserved. This project will inform the ...