Proper nutrition during adolescence is critical in ensuring long-term health and longevity. However, in the United States (U.S.), adolescents, especially those from minority, low socioeconomic status (SES), and urban backgrounds, have a poor diet. Studies report that energy-dense, nutrient-poor snacking comprises a large part of the adolescent diet. However, little is known about adolescent snacking behaviors, and there have been few attempts to intervene upon it. As such, the objectives of this dissertation are to: 1) investigate differences in the snacking behaviors of adolescents by socioeconomic status through analysis of National Health and Nutrition Examination Survey data, 2) explore factors that influence the snacking behaviors of adolescents from urban communities through interviews, and 3) assess the feasibility of a youth advocacy program promoting healthy snacking among adolescents at a Boys & Girls Club in New York City through a mixed methods process evaluation. Chapter 1 of this dissertation reviews what is currently known about snacking among adolescents and how youth advocacy can be used as a strategy to promote healthy snacking behaviors. Chapter 2 explores SES differences in foods/beverages and nutrients consumed by U.S. adolescents when snacking, utilizing National Health and Nutrition Examination Survey 2005-2018 data. Results reveal that adolescents from low SES backgrounds have poorer snacking behaviors than those from higher SES backgrounds. In Chapter 3, this dissertation aims to understand the aforementioned findings by qualitatively exploring the factors that influence snacking among adolescents from urban communities through interviews. Interviews report that the availability and accessibility of corner stores, which primarily stock energy-dense, nutrient-poor snacks, combined with urban adolescents’ high food autonomy and self-efficacy to purchase snacks, promotes unhealthy snacking behaviors. Next, based upon findings from the prior projects, a youth advocacy program promoting healthy snacking in corner stores is developed by adapting the Youth Engagement and Action for Health! (YEAH!) curriculum. Chapter 4 of this dissertation reports on the feasibility of this youth advocacy program through a mixed methods process evaluation. Findings report high rates of retention, attendance, participant engagement, and participant satisfaction. Lastly, the implications of these findings on future research, policy, and practice are discussed in Chapter 5. Overall, findings from this dissertation can be used to inform future research promoting adolescent snacking, as well as practices for engaging adolescents as change agents for their own health and the wellness of their communities.