Few instruments exist that have been used in as wide a range of music as the accordion. Though there were some earlier stabs at similar instruments, the modern squeezebox was invented in the early 19th century and has been used in everything from folk music to heavy metal. Related to the harmonica, concertina, harmonium and other free-reed instruments, the accordion suffered from unfair stereotyping for several decades but has been making a recent comeback, with increasing use in a variety of world music.
There are a number of different accordion styles available, each suited to a particular style of music. Many folk and ethnic styles use the button style of keyboard, with one or more rows of buttons, each tuned to a diatonic scale for the right hand and left-hand buttons for bass notes and major and minor triads in the appropriate keys. Some of these diatonic accordions offer push buttons that change reed sets, so that a single accordion can handle more musical keys.
There are also fully chromatic button-style accordions. These accordions, common in Eastern European and Russian music, offer a far greater range, with up to 11 octaves including the left-hand bass notes, but can be somewhat more complex to learn.
The piano accordion offers a chromatic keyboard in standard piano layout for the right hand with anywhere from 48 to 120 bass and chord buttons for the left, generally in what's known as the “Stradella” or standard bass system. For keyboard players who want to add a bit of variety to their sound, the piano accordion is a natural.
There are even MIDI accordions and controllers, most notably the Roland V-Accordion system, available in both diatonic- and piano-style, for the truly adventurous accordionist. Any way you squeeze it, an accordion can be a great addition to your musical arsenal.