Disaster scholars have long complained that their field is theory light: they are much better at doing and saying than analyzing. The paucity of theory doubtless reflects an understandable focus on case studies and practical solutions. Yet this works against big picture thinking. Consequently, both our comprehension of social suffering and our ability to mitigate it are fragmented. Communitas is exemplary here. This refers to the improvisational acts of mutual help, collective feeling and utopian desires that emerge in the wake of disasters. It has been observed for as long as there has been a sociology of disasters. Within the field, there have been numerous efforts to name and describe it. Yet there has been far less enthusiasm to theorize it, which means that the disaster literature has not adequately explained the social conditions under which communitas arises (or fails to). In this article, we synthesize numerous case studies to do so. This takes us beyond simple statements of what communitas is and what it should be called, to considerations of the conditions under which it emerges, how it should be conceptualized, the factors that might prevent communitas, and how we might encourage it. While primarily a theoretical work, the identification of communitas' facilitators and barriers have practical import for disaster risk reduction (DRR) policy as communitas has frequently proven to be a positive and potent force.