56, is a five-movement chamber piece for two violins, viola, and cello written in 1909 by the Finnish composer Jean Sibelius.

Composed between his Third and Fourth Symphony,[4] it remained "the only major work for string quartet of Sibelius's mature period".

A review in the Helsingin Sanomat noted: "The composition attracted a great deal of attention, and it is undoubtedly one of the most brilliant products in its field.

It contains "three detached, soft chords in E minor, remote from any of the previous harmonic implications",[4] to which Sibelius added the "voces intimae" in a friend's score.

The finale, "with more than a hint of folk fiddling",[4] grows in intensity by markings from Allegro to "sempre più energico" (always more energetic), described as "fiercely accented music of forceful contrasts but irresistible momentum".