Opus clavicembalisticum is a work for solo piano composed by Kaikhosru Shapurji Sorabji, completed on June 25, 1930. It is notable for its length and difficulty: at the time of its completion it was the longest piano piece in existence. Its duration is around 4 - 4½ hours, depending on tempo. Several of Sorabji's later works, such as the Symphonic Variations for Piano (which last probably about nine hours) are even longer.