Passacaglia and Fugue in C minor is an organ piece by Johann Sebastian Bach. Presumably composed early in Bach's career, it is one of his most important and well-known works, and an important influence on 19th- and 20th-century passacaglias: Robert Schumann described the variations of the passacaglia as "intertwined so ingeniously that one can never cease to be amazed."

The passacaglia is a musical form that originated in early seventeenth-century Spain and is still used today by composers. It is usually of a serious character and is typically based on a bass-ostinato and written in triple metre.