The document discusses implementation science (IS) in the context of HIV service delivery for injection drug users (IDUs), particularly focusing on a methadone treatment program in Dar es Salaam, Tanzania. It outlines frameworks for IS, emphasizing effective translation of research into practice, engaging communities, and addressing programmatic gaps to improve health outcomes for IDUs. The paper highlights the significance of targeted interventions and research to tackle HIV transmission among IDUs and optimize health services in various settings.