Harm reduction is one of the most controversial and widely discussed approaches in public health and social policy, addressing a broad range of pressing societal issues, including drug addiction, sex work, alcohol and tobacco use, and homelessness. Surprisingly, however, harm reduction has received very little philosophical scrutiny. In this article, I aim to fill this gap. First, I provide a systematic analysis of the core features and normative commitments of harm reduction. Second, I propose a novel, relational egalitarian justification for harm reduction. I argue that the provision of harm reduction services is not solely or primarily a matter of mitigating the negative consequences associated with high-risk behaviours. Rather, most fundamentally, it is the appropriate response to the status of vulnerable individuals as equal members of society.