Keyboard instrument, any musical instrument on which different notes can be sounded by pressing a series of keys, push buttons, or parallel levers. In nearly all cases in Western music the keys correspond to consecutive notes in the chromatic scale, and they run from the bass at the left to the treble at the right. This large group of instruments has assumed great importance because the keyboard enables a performer to play many notes at once as well as in close succession. This versatility enables the modern pianist or organist to play, in transcription, any work of Western music, whether it involves chordal harmonies, independent contrapuntal parts, or only a single melody.