Community-based participatory research (CBPR) explores social, structural, and physical environmental inequities through the active involvement of community members, organizational representatives, and academic researchers in all aspects of the research process, calling for a more comprehensive and integrated approach to research and practice. There has been a growing recognition of the need to meaningfully engage people who use drugs in public health research, in order to better understand a community that outsiders know little about, and this principle has been adopted by many drug user advocacy groups through the expression Nothing About Us Without Us. With this in consideration, the overall aim of this project is to engage current and former illicit drug users in a CBPR project to develop and design a prospective cohort study examining the HIV and HCV risk environment of people who use illicit drugs in Ottawa, Canada, referred to as the Ottawa Cohort Study. To accomplish this, the research team has partnered with the Drug User Advocacy League (DUAL), a peer-led advocacy group in Ottawa, Ontario, to recruit community members into a Community Advisory Committee (CAC), made up of current and former drug users and key stakeholders. The CAC will contribute to all aspects of the research development, including helping to establish research themes, developing research questions, analyzing and validating study findings, and creating a plan for KTE. Peer researchers will also be actively involved in recruitment and data collection. This project provides a new opportunity to engage marginalized current and former drug users and key stakeholders in community-based HIV research. While we have been successful in engaging a diverse group of people for the Community Advisory Committee, most members of this group have limited research knowledge or experience. In order to increase their engagement with the project and their ability to participate as informed decision-makers, CAC members will receive training in CBPR skills, research ethics, interviewing skills, data analysis, and KTE. What separates this project from other CBPR initiatives is the active engagement of drug users, including people who are HIV and HCV positive in a prospective cohort study, the integration of Peer Researchers at multiple stages of the research process, and a clear plan to evaluate the impact of this CBPR strategy on the CAC and Peer Researchers themselves. An evaluation of the CBPR process undertaken in this project will be conducted and it is expected that the CBPR methods developed and evaluated here will be used to inform models of CBPR with drug using communities in other settings across Ontario, and Canada.