Chromatic pairs are two musical notes that are a half step apart. They create tension and dissonance when played together due to their close proximity in pitch. Chromatic pairs are commonly used in music to add color and intensity to melodies and harmonies.

The phrase "musical keyboard" can apply to pianos, organs, celestas, and synthesizers; a number of pitched percussion instruments such as orchestra bells, xylophone, and marimba; and even carillions, hurdy-gurdies, and the keyboard portion of an accordion.

The organ is probably the oldest keyboard instrument, with the hydraulis or "water organ" appearing as early as the third century BCE. The clavichord and harpsichord appeared in the 14th century, with the former played by metal blades striking the strings, and the latter played by a plucking mechanism. The pianoforte was developed in the 18th century, and had the revolutionary difference of allowing the player to control the volume by striking the keys harder or softer (hence the name, meaning soft-loud).

Circular tuning, or well temperament, was developed around 1650. Before this, keyboards only sounded in tune in one key, because the intervals were tuned to pure or "meantone" intervals. Theorist Andreas Werckmeister proposed a series of tunings in which tempered fifths are of minutely different sizes, but enharmonic notes had the same pitches, allowing modulation through the circle of fifths. Bach's 1722 collection "The Well-Tempered Clavier" included preludes and fugues in all 24 major and minor keys.