This music genre was born at the end of the 19th century in the Southern United States. First performed by musicians of African American descent, it quickly becomes multicultural as it incorporates many musical influences.

Its rhythm is not uniform, it differs depending on the era and the genre. Two main forms can however be distinguished: Latin jazz (binary) and swing music (ternary).

Latin jazz is built on the same principles of music theory as classical, binary music. The eighth notes are played as written, in a regular fashion. The binary beat is unchanged.

In swing music, the binary beat notation is transformed when played: one of the eighth notes of the beat lasts two thirds of the beat, the other one lasts one third of the beat. The beat sounds ternary. Most often, the shortest eighth note is the one being stressed, highlighting the dynamic nature of the rhythm. The exact positioning of the eighth notes on the beat is subtle. The two thirds / one third rule can change depending on the playing speed of the piece: the faster the tempo, the more evenly the eighth notes are played.

The flow and accents depend on the chords and their functions in the piece. One can thus play behind the beat or ahead of the beat. Often, the second beats and the fourth beats are stressed: this process is called the afterbeat. When a rhythm is repeated multiple times, this is called a riff.

The rhythm in jazz music is purely organic, thanks to its strong ties with the harmony. It is the engine driving the musician’s improvisation.