Anglo concertinas are bisonoric, diatonic instruments. An entry level instrument has 20 buttons with 2 keys (for example C and G) arranged in a similar order to 2 diatonic harmonicas split across left and right hands. The 30 button models add accidentals to expand the key range. Ideal for playing folk tunes in common keys with melody and accompaniment. The most common key choices are C-G, G-D, D-A, and B-C.