The Well-Tempered Clavier, BWV 846–893, consists of two sets of preludes and fugues in all 24 major and minor keys for keyboard by Johann Sebastian Bach. In the composer's time, clavier referred to a variety of stringed keyboard instruments, most typically the harpsichord or clavichord, but not excluding the organ, although it is not a stringed keyboard.

A harpsichord is a musical instrument played by means of a keyboard. This activates a row of levers that turn a trigger mechanism that plucks one or more strings with a small plectrum made from quill or plastic. The strings are under tension on a soundboard, which is mounted in a wooden case; the soundboard amplifies the vibrations from the strings so that the listeners can hear it. Like a pipe organ, a harpsichord may have more than one keyboard manual, and even a pedal board. Harpsichords may also have stop buttons which add or remove additional octaves. Some harpsichords may have a buff stop, which brings a strip of buff leather or other material in contact with the strings, muting their sound to simulate the sound of a plucked lute.