Post-bop is a genre of small-combo jazz that evolved in the early to mid-1960s.
Post-bop is jazz from the mid-1960s onward that assimilates hard bop, modal jazz, avant-garde and free jazz without necessarily being immediately identifiable as any of the above. Post-bop can refer to a variety of Jazz music that is post-bebop chronologically but in the common understanding post-bop music reflects these influences: the more open approach to the jazz ensemble crystallized by the second Miles Davis Quintet, and the modal intensity of that group as well as of the classic John Coltrane Quartet.
Forms, tempos, and meters are freer, all the compositions are new, and the band members themselves are featured composers.... [A]n approach that is abstract and intense in the extreme, with space created for rhythmic and coloristic independence of the drummer—an approach that incorporated modal and chordal harmonies, flexible form, structured choruses, melodic variation, and free improvisation."
Miles Davis' second quintet was active during 1964 to 1968 and featured pianist Herbie Hancock, bassist Ron Carter, saxophonist Wayne Shorter, and drummer Tony Williams. They recorded six studio albums that, according to All About Jazz's C. Michael Bailey, introduced post-bop: E.S.P. (1965), Miles Smiles (1967), Sorcerer (1967), Nefertiti (1968), Miles in the Sky (1968), and Filles de Kilimanjaro (1968).
The abstractness and the free form of post bop music influenced fusion music in the 1970s. It transformed jazz music to another level that incorporates much more creative freedom and playing. The form free, harmonically free, and abstract post bop influenced artists to move away from the diatonic approaches and opened up the creative aspects of Jazz music. According to the book Miles Davis, Miles Smiles, and the Invention of Post Bop', "Miles Davis is really the one who started Post Bop and continued on the legacy of his own creation towards fusion and hard bop."