In simple terms, a genre is a type of spoken or written text. Genres, their typified features, and their internal variability have proven of great interest to ESP researchers. Genre analysis includes investigations of genres and their contexts. Genre-based teaching, on the other hand, involves course designs, lessons, and activities that help students learn genres in their present or future target contexts. To understand ESP's work on genre, it is helpful to appreciate what came before it in the first two decades of ESP. ESP's explicit shift toward genre came in the early 1980s. In addition to introducing the field to moves analysis, Swales established a sort of ESP theory of genre through definitions of key genre-related concepts. Swales calls genre a class of communicative events, reminding us that a genre is not itself a text but rather a category of texts. A key concept in Swales' 1990 genre definition is communicative purpose.