The bayan (Russian: бая́н) is is a type of chromatic button accordion developed in Russia in the early 20th century and named after the 11th-century bard Boyan.

It differs from the common accordions in some construction details:

 

• the reeds are larger and rectangular, instead of trapezoidal and are attached in large groups to a common plate, rather than in pairs; the plates are screwed to the reed block, rather than attached with wax, and they are not tuned with the tremolo.

• The melody-side keyboard is attached near the middle of the body (rather than at the rear).

• Register switches may be operated with the chin on some larger models. (also possible with some larger European button accordions)

• The diminished seventh chord row is shifted, so that the Gdim7 chord is where one would expect the Cdim7 chord in the Stradella bass system.

• Converter switches that go from standard preset chords to free bass (individual bass notes) are common on the larger instruments.

• Newer instruments may feature a register where every tone played actually produces a perfect fifth.

 

The differences in internal construction give the bayan a different tone color from Western instruments, and the bass has a much fuller sound. Because of their range and purity of tone, bayans are often the instrument of choice for accordion virtuosi who perform classical and contemporary classical music.

Moreover, the Russian bayan and chromatic button accordions have a much greater right-hand range than accordions with a piano keyboard: five octaves, plus a minor third (written range = E2-G7, actual range = E1-C#8).