A keyboard instrument is a musical instrument which is played using a musical keyboard. The most common of these is the piano. Other widely used keyboard instruments include organs of various types as well as other mechanical, electromechanical and electronic instruments. In common language, it is mostly used to refer to keyboard-style synthesizers.

Among the very earliest keyboard instruments are the pipe organ, hurdy gurdy, clavichord and harpsichord. The organ is without doubt the oldest of these, appearing in the 3rd century BC, though this early instrument—called hydraulis—did not use a keyboard in the modern sense. From its invention until the 14th century, the organ remained the only keyboard instrument. Often, the organ did not feature a keyboard at all, rather buttons or large levers which were operated by a whole hand. Almost every keyboard until the 15th century had naturals to each octave.

The clavichord and the harpsichord appeared during the 14th century, the clavichord probably being the earlier. The harpsichord and the clavichord were both very common until the widespread adoption of the piano in the 18th century, after which their popularity decreased. The piano was revolutionary because a pianist could vary the volume (or dynamics) of the sound by varying the vigor with which each key was struck. The piano's full name is "gravicèmbalo con piano e forte" meaning "harpsichord with soft and loud" but can be shortened to "piano-forte", which means "soft-loud" in Italian.

John Milton Cage Jr. (September 5, 1912 – August 12, 1992) was an American composer, music theorist, writer, and artist. A pioneer of indeterminacy in music, electroacoustic music, and non-standard use of musical instruments, Cage was one of the leading figures of the post-war avant-garde. Critics have lauded him as one of the most influential American composers of the 20th century. He was also instrumental in the development of modern dance, mostly through his association with choreographer Merce Cunningham, who was also Cage's romantic partner for most of their lives.

Cage is perhaps best known for his 1952 composition 4′33″, which is performed in the absence of deliberate sound; musicians who present the work do nothing aside from being present for the duration specified by the title. The content of the composition is not "four minutes and 33 seconds of silence," as is sometimes assumed, but rather the sounds of the environment heard by the audience during performance. The work's challenge to assumed definitions about musicianship and musical experience made it a popular and controversial topic both in musicology and the broader aesthetics of art and performance. Cage was also a pioneer of the prepared piano (a piano with its sound altered by objects placed between or on its strings or hammers), for which he wrote numerous dance-related works and a few concert pieces. The best known of these is Sonatas and Interludes (1946–48).