It is the modernist wisdom that each art or medium should be defined in its own terms, so as to delimit it from other arts or media, while also arriving at certain conclusions as to the ‘message’ of the medium in question and its preferred subject-matters. This tradition has often been criticized for an inherent essentialism, and a less prescriptive approach is proposed in the following article – which, while taking the interaction between the different arts and media into account, also attempts to understand this in its historical perspective. The author, Klaus Ulrich Militz, concentrates mainly on the interrelations between the audio-visual performing arts of theatre, cinema, and television, and refers in particular to a number of artistic approaches to theatre which appear to be based on media interplay as a major source of aesthetic innovation. He also includes some crucial statements by theatre artists, suggesting different ways in which they came to locate their aesthetic positions. Klaus Ulrich Militz is a member of the media research group at the University of Edinburgh, and is currently completing his doctoral thesis on the work of Rainer Werner Fassbinder.