This study tests the efficacy of the MASLIHAT Intervention to reduce risky drug, alcohol, and sexual behavior among Tajik male labor migrants in Moscow who inject drugs compared with a control intervention in a parallel design cluster-randomized trial. The control condition is designed to be equal to the intervention condition in the number of sessions, duration, and interest level. In both conditions, we trained Tajik migrant MWID as peer educators to deliver the intervention to their network members both during the five-week training and after completion. We assessed changes in drug, alcohol, and sexual risk behavior at 3, 6, 9 and 12 months post-intervention, and compared effects for MASLIHAT and control group participants, and their network members. We also examined mechanisms of behavior change among MASLIHAT participants, including purported mediators and potential moderators. We assessed changes in HIV knowledge, risk awareness, prevention self-efficacy, psychosocial well-being, and behavioral norms among participants and network members, and tested associations with injection drug use (IDU) social network interactions and mediation of behavior change outcomes. We hypothesize that the MASLIHAT intervention will influence behavior of both peer educators and network members by increasing knowledge and awareness of HIV transmission risks, modifying behavioral norms, and improving self-efficacy.