The fact that the mass media constitute such a ubiquitous presence in contemporary life often leads to the assumption that medium or media emerged as a specific issue only with the advent of mass media. The question of medium is today almost totally subsumed within discussions of the mass media. In this context, it is always regarded as plural. Yet the issue of the medium became a central concern of modernist art almost a century and a half ago. This collection of essays seeks to reopen this long history of exploration and engagement and to scrutinize the role of the medium in areas as diverse as modernist, contemporary, and avant-garde art, photography, cinema, and architecture, as well as in the more familiar guises of electronic media including television and computer games.