Guillermo Gregorio (born May 1, 1941, Buenos Aires) is an Argentine jazz and free improvisation clarinetist, saxophonist, and composer. Gregorio was born into a musical family. He became interested in experimental music in the early 1960s, culminating in his Unheard Music project (later released on the album Otra Música: Tape Music, Fluxus, and the Improvisation in Buenos Aires 1963-1970). In addition to his musical work, Gregorio also worked as a professor of architecture and as an author on classical and modern music avant-garde forms.