The ongoing mental health crisis of children and adolescents was only worsened by the confluence of issues brought about by the COVID-19 pandemic (Hiebert & Kortes-Miller, 2021) with continued growing rates of anxiety and depression as well as elevations in suicidal ideation and thoughts of self-harm among today's youth (Reinert et al., 2021). Given the popularity and reach of sport, along with promising research on positive developmental impacts, The Women's Sport Foundation (WSF) commissioned this report to examine the relationship between sport participation and mental health in adolescent girls. It set out to examine: (1) What is the relationship between sport participation and mental health in adolescent girls? (2) How do the characteristics of the sport environment affect the relationship between sport participation and mental health? and (3) Does the relationship between sport and mental health differ across contexts and demographic groups? [Additional funding from Nike.]