The harm reduction approach has become a viable framework within the field of addictions, yet there is limited understanding about how this approach is implemented in practice. For people who are homeless and have co-occurring psychiatric and substance use disorders, the Housing First model has shown promising results in employing such an approach. This qualitative study utilizes ethnographic methods to explore case managers' use of harm reduction within Housing First with a specific focus on the consumer–provider relationship. Analysis of observational data and in-depth interviews with providers and consumers revealed how communication between the two regarding the consumer's substance use interacted with the consumer–provider relationship.