A septet is a formation containing exactly seven members. It is commonly associated with musical groups, but can be applied to any situation where seven similar or related objects are considered a single unit.

In jazz music a septet is any group of seven players, usually containing a drum set (pedal bass, snaredrum sometimes brushed, top hat cymbal, brushed cymbal), string bass or electric bass, and groups of one or two of the following instruments, guitar, trumpet, saxophone, clarinet, or trombone.

In classical music, a septet is either a composition for performance by seven musicians, or a group of seven musicians who perform such a work. One of the most famous classical septets is the Septet in E-flat major, Op. 20, by Ludwig van Beethoven, composed around 1799-1900, for clarinet, bassoon, horn, violin, viola, cello, and double bass. The Septet in E-flat major, Op. 65, for trumpet, piano, string quartet, and double bass by Camille Saint-Saens from 1881 is regarded by some critics as one of that composer's greatest works. The modern composer Bohuslav Martinu wrote three septets: a group of six dances called Les Rondes for oboe, clarinet, bassoon, trumpet, two violins, and piano (1930); a piece called Serenade No.3 for oboe, clarinet, four violins, and cello (1932); and a Fantasie for theremin, oboe, piano, and string quartet (1944). Darius Milhaud composed a String Septet in 1964 for string sextet and double bass.