The purpose of this paper is to present a critical analysis of the concept of warm-up by tracing its historical development from early colloquial uses, through its uses in drama, to its current use in psychodrama. It begins by examining the usage of warm-up in the early twentieth century, followed by its usage in general theatre, impromptu theatre, therapeutic theatre and psychodrama. It follows the particular usage to which Moreno put it, and shows how this led to its educative and therapeutic usages. It shows how warm-up is principally valued for its utility amongst practitioners as a workable heuristic. It concludes that, as a heuristic in psychodrama, it has transmogrified into four importantly different concepts, which, although evident in its use, have not been explicitly recognised, limiting its practical and theoretical usefulness.