Sexual minority youth (SMY; i.e., gay/lesbian, bisexual, or questioning) are more likely to use substances (e.g., tobacco, alcohol, marijuana) and engage in disordered weight behaviors (e.g., purging) than their heterosexual peers. These health disparities emerge in early adolescence and place SMY at disproportionate risk for developing cancer, cardiovascular disease, substance-related injuries and disorders, eating disorders, and obesity. SMY may engage in substance use and disordered weight behaviors to mitigate stress. It is also possible that these behaviors are adopted and maintained because they help to build connections with SMY peers though conformity to perceived sexual minority substance use and body image norms. The operation of these stress and socialization pathways is likely contingent on the diverse social settings SMY traverse and the capacity of settings to provide safety, connectedness, structure, and salubrious health behavior norms. However, there is a dearth of empirical research examining characteristics and activities of settings that promote health in SMY. Although limited research suggests that the presence of formally organized support settings may protect against negative affect and sociality, there is a lack of understanding of how and why such support settings have a protective effect or whether these protective effects will also extend to substance use and disordered weight behaviors. In the planned K01 research I will use prospective longitudinal survey data and ecological momentary assessment (EMA) techniques to investigate characteristics and activities in settings that mitigate minority stress and protect against substance use and disordered weight behaviors among SMY. Data will come from (1) the Growing Up Today Study -- a national cohort of over 16,000 adolescents and young adults -- to assess overall associations between contextual characteristics, stress, and substance use and disordered weight behaviors; and (2) a cohort of 60 SMY recruited from SMY-serving organizations and via respondent-driven sampling techniques in the Boston area to examine the dynamics of the settings SMY traverse and their temporal connections to minority stress, substance use, and disordered weight behaviors. To facilitate such research, I must gain training in community-based participatory research (CBPR) and prevention science, EMA study design and analysis, and diverse longitudinal statistical methods (e.g., finite mixture modeling with intensive longitudinal data) for analyzing the connections between contextual interactions and health behaviors. CBPR with SMY can promote sustainable positive change by generating detailed information about the contextual factors contributing to health disparities, by building the leadership skills and feelings of self-efficacy in SMY, and by bolstering social support infrastructure within SMY-serving organizations. The proposed research will identify modifiable contextual-level leverage points for preventive interventions and position me for a career as a prevention scientist.