With the advent of montage and collage, new aesthetic categories have emerged that define the beginning of artistic modernity. The "papiers collés" created by the Futurists and Cubists mark a common tendency to transcend the boundaries of art, leading on one hand musically from Russolo's "arte dei rumori" to "musique concrète" and the acoustic art of the present, while on the other hand approaching music as sound art. In contrast, the sensory collisions of the collage invented by Max Ernst in the 1920s can only be partially grasped musically. The resulting engagement with already occupied materials leads many composers to reflect on reality and aesthetic illusion, on the significance of reception for production, on finding and inventing - in short: to "music about music.".