We propose a 5-year implementation science project in Vietnam, aiming to enhance the role of commune health workers (CHWs) in HIV and drug use prevention and treatment. We plan to demonstrate the process of development, implementation, and evaluation of an integrated intervention for CHWs, IDUs, and their family members (FMs) in Vietnam. In Phase 1, intervention topics, format, delivery procedures, and supporting materials will be developed through a series of focus group discussions. In Phase 2, implementation pilot and process evaluation will be conducted to collect feedback from participating CHWs, IDUs and their FMs by in- depth interviews in two commune health centers. In Phase 3, we will conduct an intervention trial (CHW CARE intervention) in 60 commune health centers (5 CHWs, 15 IDUs and 10 FMs from each commune center), totaling 300 CHWs; 900 IDUs and 600 FMs. Randomization will occur at the commune level (30 communes assigned to the intervention group; 30 communes assigned to the control group). At each commune assigned to the intervention, the intervention will be delivered to CHWs first, and the participating CHWs will be required to conduct individual and group sessions with IDUs and FMs in their communes. The efficacy of the intervention will be assessed at baseline, 3, 6, 9, and 12-month follow-ups by comparing outcome measures of CHWs, IDUs and FMs in the intervention group to those in the control group. Relationships between the intervention outcomes of CHWs, IDUs and FMs will also be explored.