This article discusses the possibility and desirability of engaging with a non-state armed group, such as the Islamic State (IS), on the topic of international humanitarian law (IHL). It first describes the structure and ideology of IS, and then, it proceeds to analyse the law applicable to armed groups as well as the challenges encountered when engaging these actors. In particular, it considers when such groups reject IHL as a common normative framework regulating armed conflicts. The last section of this article examines direct and indirect ways humanitarian actors have engaged armed groups, such as IS.