This chapter discusses the progression of visual music and related audio-visual artworks through the 20th Century and considers the next steps for this field of research. The principles of visual music are described, with reference to the films of early pioneers such as John Whitney. A further exploration of the wider spectrum of subsequent work in various audio-visual art forms is then given. These include visualisations, light synthesizers, VJ performances, digital audio-visual artworks, projection mapping artworks, and interactive visual music artworks. Through consideration of visual music as a continuum of related work, the authors consider the Holophonor, a fictional audio-visual instrument, as an example of the ideal visual music ins...