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A harpsichord is a musical instrument played by means of a keyboard, a row of levers which the player presses. When the player presses one or more keys, this triggers a mechanism, which plucks one or more strings with a small quill. Unlike the piano, a keyboard instrument invented in 1700, on which harder and softer presses of the keys produce louder and quieter sounds, on the harpsichord, harder or softer pressing of the keys does not change the volume (loudness) or tone of the notes.

During the Baroque music era, the harpsichord was one of the key instruments used for chordal accompaniment and to play the basso continuo parts, both in small chamber music ensembles and in Baroque orchestra and opera orchestras (the other important instrument for basso continuo was the pipe organ). At the same time, the harpsichord was also used during this era as a solo instrument, to play virtuoso concertos. The harpsichord differs from the pipe organ in that the pipe organ uses metal and wood pipes and air to produce sound, rather than strings, and in that with an organ, a note sustains for as long as the player depresses the key; in contrast, on harpsichord, the sound decreases in loudness shortly after it is played.

"Harpsichord" designates the whole family of similar plucked keyboard instruments, including the smaller virginals, muselar, and spinet. The harpsichord was widely used in Renaissance and Baroque music. During the late 18th century, it gradually disappeared from the musical scene, with the rise of the piano. In the 20th century, it made a resurgence, being used in historically informed performances of older music, in compositions, and in some styles of popular music.

Harpsichords vary in size and shape, but all have the same basic mechanism. The player depresses a key that rocks over a pivot in the middle of its length. The other end of the key lifts a jack (a long strip of wood) that holds a small plectrum (a wedge-shaped piece of quill, often plastic in the 2010s), which plucks the string. When the player releases the key, the far end returns to its rest position, and the jack falls back. The plectrum, mounted on a tongue that can swivel backwards away from the string, passes the string without plucking it again. As the key reaches its rest position, a felt damper atop the jack stops the string's vibrations. These basic principles are explained in detail below.

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