This report from the Canadian Observatory on Homelessness looks at the critical role of prevention in comprehensive system response to youth homelessness. It outlines evidence-based and informed program areas to help communities and governments implement plans to prevent and end youth homelessness. The authors consider how the public health field contemplates and operationalizes prevention strategies when the main goal of prevention is to minimize harm to individuals or communities by lowering the risk and outcomes of disease, illness, and injury. The public health approach identifies risk and protective factors and implements universal interventions for average risk and targeted interventions for higher or imminent risk. The authors contend that prevention for youth homelessness is a housing-led response. (author abstract modified)