There are two basic bass types of accordion: 

• The standard-bass accordion, on which each button of the left-hand manual represents a fixed chord, and the buttons (or chords) commonly are arranged in six rows. 
• The free-bass accordion, on which the left-hand manual has no chords at all, its buttons (usually in three rows) representing single pitches chromatically graduated in a range up to six-and-a-half octaves. 

The standard-bass accordion is the most widely played and traditionally has been associated with ethnic, folk, and pop music. The free-bass accordion has been developed mainly as a concert-music instrument, its repertoire consisting for the most part of transcriptions of the classics and original works by contemporary composers.