Methods of incorporating jazz in opera range from using simple blue notes and fox-trot rhythms, to utilizing jazz instruments, to employing elaborate passages of improvisation. Current definitions of "jazz opera" do not consider variations in the genre, which, because of their evolving nature and the varied background of their composers, are diverse. This study attempts to collectively discuss these third-stream works. Jazz rhythms and harmonies first appeared in the 1920s in the works of Gershwin, Harling, Krenek, and Freeman. In 1966, Gunther Schuller was the first composer to use improvisation in an opera, which has become the primary distinguishing factor. There has since been a tremendous interest in this genre by such jazz musicians as Dave Burrell, Anthony Davis, Duke Ellington, Max Roach, Anthony Braxton, George Gruntz, and Jon Faddis.