Bop, also known as bebop or rebop is a form of jazz that was created as a revolt against the restrictions on creative freedom that were typical of the big bands of the swing era. In many of the big bands the solos were typically very short. This upset many soloists as there wasn't room for experimentation. Bebop was a natural response to this. Most bebop players turned to small combos where there was a lot more room for innovative improvisation.

There is no defining moment when bop was born. Rather, many unrelated events helped with the birth of bop. Bop developed in many locals including Kansas City and St. Louis. It solidified as a jazz form in New York in the early 1940's. Bop first made its appearances in the playing of Charlie Parker, Dizzy Gillespie, and Thelonious Monk. These three musicians played together and refined a very complex kind of music.

Bebop improvisations are composed mostly of eighth-note and sixteenth-note figures which seem jumpy and include many twists and turns of melody. Also, it often includes large intervals between notes and abrupt changes of direction with regards to the melody. Bebop musicians based their improvisation around chord changes rather than just embelishing a melody. Often they enriched a piece by adding chords to the chord progression. This is known as substitution. Sometimes they would also alter the existing chords of a piece by flatting the 5 of the chord, or adding the 9 and 13 to the chord. This added to the complexity of bebop improvisation. One popular method of writing bebop tunes, utilized by Charlie Parker and many others, was to take the chord changes from an existing piece and write or improvise a new melody over those changes. This allowed a rhythm section to play a tune that they might have never heard before.

Bebop was not nearly as popular as swing had been. There are several explanations for this fact. One explanation is that bop music was a lot more complicated than swing and therefore made it a hard music for the general public to appreciate. Where as swing musicians pieces would sound the same in concert as in recordings a bop musician might never play a piece the same way twice. Another argument is that bop lacked popularity because there weren't that many bop singers. The argument is that people relate more to music with lyrics. Related to this argument is the fact that swing was popular dance music while bop was not. All this resulted in the fact that when Charlie Parker died in 1955 he was no where near as well known as Benny Goodman or Duke Ellington. In the long run, however, Charlie Parker, Dizzy Gillespie, and Thelonious Monk, the three main figures in bop played a very significant part in the development of jazz.

This summary by Sean Glass using information from Jazz by Tanner, Megill and Gerow and Jazz Styles by Mark C. Gridley.