Housing First (HF) is an increasingly widespread and influential response to chronic homelessness. Programs using an HF approach typically rely on market apartments to house homeless clients as rapidly as possible. This reliance means HF programs are dependent on the availability and affordability of market housing. Little attention has been given to how shortages of affordable rental housing influence the practice of HF. To address this gap, we undertook qualitative research in Alberta, Canada. Interviews with service providers revealed that high rents and low vacancy rates had profound impacts on program operations, and complicated efforts to follow HF principles. Clients often experienced delays in being housed and felt pressure to accept the first apartment they were offered. In response, HF programs devoted resources to improve relationships with landlords. Ultimately, however, reliance on market housing undermined programs’ ability to fulfil the potential of HF in the Alberta context.