Gustav Leonhardt (born May 30, 1928) is a highly acclaimed Dutch keyboard player, conductor, musicologist, teacher and editor. Leonhardt has been a leader in the movement to perform music on period instruments. The keyboard instruments on which he has performed and recorded include the harpsichord, organ, claviorganum (a combination of a harpsichord and an organ), and fortepiano.

From 1947 to 1950 Gustav Leonhardt studied organ and harpsichord with Eduard Müller at the Schola Cantorum in Basel. He made his debut as a harpsichordist in Vienna in 1950 and studied musicology there. He served as professor of harpsichord at the Academy of Music from 1952 to 1955 and as professor of harpsichord at the Amsterdam Conservatory from 1954. He also was a church organist.
Leonhardt made his first recordings of Johann Sebastian Bach's works for harpsichord in the early 1950’s. These recordings established his reputation as a fine harpsichordist and brilliant Bach interpreter. In 1954 he led the Leonhard Baroque Ensemble with the great English counter-tenor Alfred Deller in a pioneering recording of two Bach cantatas. The Ensemble included his wife Marie Leonhardt and Eduard Melkus (violins), Alice Hoffelner (viola), Nikolaus Harnoncourt (cello), and Michel Piguet (oboe). Leonhardt's interpretations of the harpsichord works of Francois Couperin are particularly insightful - his phrasing is unique and authentic to the French Baroque period, and his conformance to the improvisational style intended by Couperin is exceptional.
Leonhardt is also an exceptional interpretor of the harpsichord works of Francois Couperin, although many of his Couperin recordings are now, unfortunately, out of print.
Although Leonhardt has performed and conducted a diversity of music from the Baroque and Classical music era periods, he is particularly known for his recordings with Harnoncourt of Bach's cantatas spanning twenty years, from 1971 to 1990.