The bandoneon is a type of concertina particularly popular in Argentina and Uruguay. Although it is the essential voice of Tango music, it was actually invented in Germany by Heinrich Band in the mid-19th century. Originally intended for religious and popular music of the time, it was brought to the Rio de la Plata region by sailors and immigrants. The instrument is bellows-driven and features buttons on both the right and left sides. Most bandoneons are 'bisonoric,' meaning a single button produces a different note depending on whether the bellows are being pushed or pulled. This unique characteristic gives the instrument its signature staccato and sighing sound, which mimics human emotion. Mastering the bandoneon is notoriously difficult because the player must essentially memorize four different keyboard layouts (two for each hand, depending on the bellows' direction).