This chapter focuses on the role of transnational private military and security companies (PMSCs) in humanitarian settings, which according to Frederik Rosén, ‘[b]y the millennium, […] had gained a solid foothold in the humanitarian space and in post-confl ict settings’ (Rosén 2008: 80). The relationships that PMSCs maintain with other humanitarian actors take multiple forms. First, PMSCs often operate in the same geographical space where traditional humanitarian organizations or agencies such as international governmental and non-governmental organizations deliver services. Second, these actors contract PMSCs to carry out certain services such as training, risk analysis or physical security. Third, PMSCs claim to deliver humanitarian services themselves. These diff erent types of interaction have to be understood against the backdrop of at least two recent and related trends: First, the privatization of security more generally, which refers to the heightened involvement of private actors in confl ict zones of which PMSCs are one, but not the only type; and second, the increasing insecurity of actors providing humanitarian assistance in the context of armed confl icts..