Diatonic button accordion

A melodeon or diatonic button accordion is a member of the free-reed aerophone family of musical instruments. It is a type of button accordion on which the melody-side keyboard contains one or more rows of buttons, with each row producing the notes of a single diatonicscale. The buttons on the bass-side keyboard are most commonly arranged in pairs, with one button of a pair sounding the fundamental of a chord and the other the corresponding major triad (or, sometimes, minor triad).

Diatonic button accordions are popular in many countries, and used mainly for playing popular music and traditional folk music, and modern offshoots of these genres.