Project summary Friendships typically protect youth against the development of emotional problems and may be especially important sources of support for youth who experience psychological distress. Troubling, however, is research documenting the phenomenon of contagion, or the process by which friends of suicidal, self-injurious, or depressed youth are at markedly increased risk for developing these problems themselves. While having distressed peers confers risk for increases in adolescents’ distress over time, no studies have closely examined contagion of suicide and non-suicidal self-injury (NSSI) within adolescent social relationships, and very few studies have examined depression contagion. Further, little is known about what factors may predict susceptibility and resilience to contagion, and mechanisms of contagion are likewise understudied. The proposed multi-method, longitudinal study examines contagion of suicidality, NSSI, and depression in a large sample of rural, at-risk adolescents in grades 5-12. The research proposes new and novel susceptibility markers for examination including overactive empathy, media exposure (e.g., 13 Reasons Why, Netflix, 2017), and parasocial interaction (e.g., one-sided, emotional relationship with media figures). The study also examines co-rumination (Rose, 2002) as a hypothesized mechanism for contagion effects across all of these conditions. Self-report, peer-report, observational, and event-sampling data will be collected over multiple time points during one school year. The use of multiple methods will provide detailed, temporal information about the processes involved in contagion of suicidality, NSSI, and depression aid in identifying the characteristics of those most susceptible. What is more, the sudden onset of COVID-19 during spring 2019 in the US presents unexpected opportunities to explore adolescents’ socioemotional adjustment (e.g., isolation, loneliness, social interaction) prior to and immediately after the onset of COVID-19 (Cohort 1, 2019-2020), during the peak of COVID-19 (Cohort 2, 2020-2021), and during the period in which the COVID-19 vaccine is increasingly available (Cohort 3, 2021-2022).