Single session therapy is a specific form of therapy conducted by professionals who seek to use their existing skill sets and knowledge base to address clients’ presenting concerns, within one session. The session takes place with the understanding that the session might be the only one. Such single session services are currently expanding in a number of high income countries. This paper calls attention to this therapy for potential adaptation to acute emergency settings, in low and middle income countries, where offering one session may be the only option. This paper describes: (a) single session therapy as adapted in recent emergency settings; (b) the single session model in high income countries; (c) its relationship with psychological first aid; (d) the development of the model and its evidence base; and (e) the model as an intervention and a service. While single session therapy holds promise for work in humanitarian settings, there is still a need for randomised controlled studies in humanitarian settings before this therapy may be considered as recommended, evidence based, humanitarian practice.