Reply #48: It's a style that emerged during the early and mid sixties.

[MilesColtrane]

The musicians who were working in the style that Charlie Parker, Dizzy Gillespie, Thelonius Monk, and others had developed during the 50's began to incorporate the influence of modal harmonies, free jazz, and what would later be called world music into the mix.

There is some blurring between what is considered post bop and hard bop, but post bop had a more open sound. The forms were less rigid and the harmonic structure of the music relied less on functional (traditional standard song type) harmony. Soloists would sometimes abandon the written chord changes in their improvisations. Rhythm sections would imply other time signatures or they would not play the time at some points, opting for a more free approach.

The major players in this then young style were Wayne Shorter, Herbie Hancock, Joe Henderson, McCoy Tyner, and others.

Many of these artists were on the Blue Note record label.