These performers provide accompaniment by playing chords and rhythms that outline the song structure and complement the soloist.
In avant-garde and free jazz idioms, the separation of soloist and band is reduced, and there is license, or even a requirement, for the abandoning of chords, scales and rhythmic meters.
In the 1930s, heavily arranged dance-oriented swing big bands, Kansas City jazz, a hard-swinging, bluesy, improvisational style and Gypsy jazz (a style that emphasized musette waltzes) were the prominent styles.
Bebop emerged in the 1940s, shifting jazz from danceable popular music toward a more challenging "musician's music" which was played at faster tempos and used more chord-based improvisation.
Since the 1920s Jazz Age, jazz has become recognized as a major form of musical expression.
It then emerged in the form of independent traditional and popular musical styles, all linked by the common bonds of African-American and European-American musical parentage with a performance orientation.
Subsequent styles such as modal jazz abandoned the strict notion of a chord progression, allowing the individual musicians to improvise even more freely within the context of a given scale or mode.
In many forms of jazz, a soloist is often supported by a rhythm section consisting of one or more chordal instruments (piano, guitar, etc.), double bass playing the basslines and drum kit.
The 1950s saw the emergence of free jazz, which explored playing without regular meter, beat and formal structures, and in the mid-1950s, hard bop emerged, which introduced influences from rhythm and blues, gospel, and blues, especially in the saxophone and piano playing.
Modal jazz developed in the late 1950s, using the mode, or musical scale, as the basis of musical structure and improvisation.