Causal mediating processes were examined using qualitative methods to evaluate a tobacco-use prevention program for adolescents in India, Project MYTRI (Mobilizing Youth for Tobacco-Related Initiatives in India). Interviews were conducted with Project MYTRI leaders and staff persons. The focus of the interviews was to learn about the program implementation and to characterize how Project MYTRI classroom sessions altered student-level psychosocial risk factors (mediators) to prevent or reduce tobacco use among students in intervention schools in Delhi and Chennai. From qualitative analysis, key mediating variables were identified (students’ tobacco knowledge, skills development, beliefs about tobacco, intentional beliefs, advocacy beliefs, and self-efficacy beliefs), a qualitative mediation path model was drawn, causal processes were described, and contextual influences (potential moderators) were explained. The qualitative findings complemented the results of statistical mediation analysis, yielding a detailed and contextualized description of how Project MYTRI affected students.