Dixieland and swing stylists improvise melodically and bop, cool and hard bop players follow chord structures in their solos. Free Jazz was a radical departure from past styles for typically after playing a quick theme, the soloist does not have to follow any progression or structure and can go in any unpredictable direction. When Ornette Coleman largely introduced Free Jazz to New York audiences (although Cecil Taylor had preceded him with less publicity), many of the bop musicians and fans debated about whether what was being played would even qualify as music; the radicals had become conservatives in less than 15 years. Free Jazz, which overlaps with the avant-garde, remains a controversial and mostly underground style, influencing the modern mainstream while often being ignored.

Avant-garde Jazz differs from Free Jazz in that it has more structure in the ensembles (more of a "game plan") although the individual improvisations are generally just as free of conventional rules. In the best Avant-Garde performances it is difficult to tell when compositions end and improvisations begin; the goal is to have the solos be an outgrowth of the arrangement. As with Free Jazz, the Avant-Garde came of age in the 1960's and has continued almost unnoticed as a menacing force in the jazz underground, scorned by the mainstream that it influences. Among its founders in the mid-to-late 1950's were pianist Cecil Taylor, altoist Ornette Coleman and keyboardist-bandleader Sun Ra. John Coltrane became the avant-garde's most popular (and influential) figure and from the mid-1960's on the avant-garde innovators made a major impact on jazz, helping to push the music beyond bebop.