A jazz band (jazz ensemble or jazz combo) is a musical ensemble that plays jazz music. Jazz bands vary in the quantity of its members and the style of jazz that they play but it is common to find a jazz band made up of a rhythm section and a horn section.

The size of a jazz band is closely related to the style of jazz they play as well as the type of venues in which they play. Smaller jazz bands, also known as combos, are common in night clubs and other small venues and will be made up of three to seven musicians; whereas big bands are found in dance halls and other larger venues.

Jazz bands can vary in size from a big band, to a smaller trio or quartet. Some bands use vocalists, while others are purely instrumental groups.

Jazz bands and their composition have changed many times throughout the years, just as the music itself changes with personal interpretation and improvisation of its performers.

It is common for musicians in a combo to perform their music from memory. The improvisational nature of these performances make every show unique.

The rhythm section consists of the percussion, double bass or bass guitar, and usually at least one instrument capable of playing chords, such as a piano, guitar, Hammond organ or vibraphone; most will usually have more than one of these. The standard rhythm section is piano, bass, and drums.

The horn section consists of a woodwind section and a brass section, which play the melody.

The banjo has been used in jazz since the earliest jazz bands. The earliest use of the banjo in a jazz band was by Frank Duson in 1917, however Laurence Marrero claims it became popular in 1915.