Project Summary People who inject drugs (PWID) are at high risk for HIV infection and transmission as well as fatal opioid overdoses. The goal of this R34 is to pilot the key components necessary for a larger setting-based randomized clinical trial (RCT) for increasing medication-assisted treatment (MAT) and HIV medical care and medication adherence. In the proposed study, we will recruit 80 index PWID (half HIV seropositive) who have: 1) been on MAT for at least one year, 2) are able to recruit active network members who use drugs, and 3) are willing to promote MAT to these PWID. Based on our pilot data, we anticipate these 80 index participants to be able to recruit approximately 160 network members (two each) for the study intervention. After the baseline assessment of the indexes and network members, the indexes and their respective network members will be randomly assigned to the experimental intervention or the comparison condition. In the experimental intervention, the indexes will be trained on how to work with their network members to promote MAT and HIV care, including ART adherence, for drug network members living with HIV. All study participants will be assessed at 3 months with surveys and drug testing. Outcomes will include MAT uptake among network members, retention on methadone amongst indexes and network members, reduced HIV seroconversions among network members, reduced illicit drug use among all study participants, and linkage to HIV medical care and ART adherence among network participants who are living with HIV. Based on findings from our prior studies, we also anticipate that the health behaviors of the index participants randomized to the experimental group will improve due to their peer education activities. We will conduct qualitative process and outcomes interviews with 10 indexes in the experimental intervention condition and 10 network members. We will also interview 8 MAT and HIV clinic staff members to assess their perspectives on intervention feasibility and acceptably. Given the scope of the opioid epidemic and continued HIV epidemic among PWID, development of novel interventions to increase MAT uptake and retention is critical.