In the early twentieth century, jazz emerged out of the styles of ragtime, dixieland, boogie-woogie, and rhythm and blues music. The looseness and emphasis on creativity of all of these styles contributed to the emphasis on improvisation found in jazz music. It can also be seen as an instrumental expression of the call-and-response dynamic found in old working songs.
Some styles of jazz are known more for improvisation than others. For example, swing and big band music employ solos and improvisation, but are thought of more as dance music. Bebop, on the other hand, is primarily known for the improvisatory genius of musicians such as Dizzy Gillespie, Charlie "Bird" Parker, and Bud Powell. Major post-bop improvisers include figures such as Miles Davis, John Coltrane, and Bill Evans.
The structure of improvisation is based on the elaboration of chord progressions. In a quartet, as an example, the bass and piano will play through the basic melody while the saxophonist or trumpeter improves over them. The soloist progresses through the same chords but in an improvised way that is compatible with, rather than a direct expression of, the basic chord progression. Another approach to improvisation is based on modal scales rather than chords, as on Miles Davis's famous album Kind of Blue (1959).
Scat singing is a sub-genre of jazz improvisation, in which a vocalist will sing with meaningless sounds rather than words. This allows both singer and audience to focus more on the rhythm and feel of the improvisation rather than the narrative structure. Louis Armstrong and Ella Fitzgerald were two of the great popularizers of scat singing.
In the 1950s and 1960s, jazz progressed into new territories such as free jazz and fusion. Free jazz, epitomized by innovators such as Ornette Coleman, Cecil Taylor, and Sun Ra, takes the form to and sometimes beyond its logical limits, often incorporating dissonance, difficult rhythms, and atonality such as saxophone screeches. Fusion, popularized in the late 1960s by Miles Davis, brings in the predictable rhythmic patterns and electronic instruments of other forms of music, such as rock and funk, but maintains the interior space that allows for improvisation.