The Downtown Eastside (DTES) of Vancouver, Canada has been the epicentre of HIV, hepatitis C and drug overdose related to People who inject drugs (PWIDs) since the mid1990s. In response to the growing government inaction, numbers of peer-run organizations were formed. This dissertation was conducted to capture the genesis and influence of peer drug users, their networks and harm reduction programs over the past 18 years in shaping the neighborhood. Semi-structured qualitative interviews were conducted with peers from various harm reduction volunteer locations in the DTES. Moreover, various drug users were recruited from a controversial harm reduction program in the DTES that provides pharmaceutical heroin. Interviews were analyzed thematically using two methods of coding analysis. Findings suggest that peers were taking on important education and safety roles, and were able to alter the behaviour, attitude, and intention of injection drug users within the DTES area of the city. Further, peer injection drug users were able to reach individuals who were reluctant to seek medical help, housing, and prevention services. Peers serve as an agent of change in the DTES to disseminate information and risk reduction skills to the most marginalized people. Peer drug users have not only been able to change the discriminatory rhetoric but they have been able to reduce the suffering that drug users have endured as a consequence of the war on drugs. Attending heroin trials in Vancouver has been particularly effective in creating a unique microenvironment where PWIDs who have attended heroin trials have been able to form a collective identity advocating for their rights. In physical terms, the DTES has become cleaner and safer for its residents because of availability of an injection facility and numerous peer-run harm reduction programs. In conceptual terms, PWIDs are less likely to experience discrimination by the city, hospital, and police. Moreover, the residents in the new DTES are more likely to be involved in their civic issues and raise concerns in a new political arena. Peer-run harm reduction programs have given a voice to the most marginalized members of society who otherwise would not be represented. The result of this dissertation and costing analyses conducted point to the need for the expansion of the peer and harm reduction programs beyond the current location in the DTES to other locations in Canada such as Montreal, Ottawa, Toronto, Saskatoon and Victoria.