A type of chromatic button accordion developed in Russia in the early 20th century.

The bayan differs from western chromatic button accordions in some details of construction: 

• reeds are broader and rectangular (rather than trapezoidal)
• reeds are often attached in large groups to a common plate (rather than in pairs) - the plates are screwed to the reed block
• the melody-side keyboard is attached near the middle of the body (rather than at the rear)
• reeds are generally not tuned with tremolo
• register switches may be operated with the chin on some larger models
• the diminished chord row is shifted, so that the diminished G chord is where one would expect the diminished C 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 colour from Western instruments, and the bass has a much fuller sound.