Schoenberg's music became very atonal (not in any key). Eventually he developed what he called twelve tone music. This was atonal music which was organized by putting the notes of a musical idea in a particular order which could be changed in many ways during the piece. This way of organizing music is called “serialism” (a “series” is a “row of things”). Many composers were influenced by Schoenberg, especially Alban Berg and Anton von Webern.