Fantasia No. 3 in D minor, K. 397 (Fantasy in English, Fantasie in German) is a piece of music for solo piano composed by Wolfgang Amadeus Mozart in 1782. Despite being unfinished at Mozart's death, the piece is nonetheless one of his more popular compositions for the piano. Because of its somewhat unusual rhythm, its constantly changing tempo (seven different tempi occur throughout the piece, some of which are quite fast, including the three meter-less cadenzas), and its apparent lack of any recognizable musical form (as indicated by the "Fantasy" title). It does in fact closely follow sonata form. The Fantasia is considered to be a relatively challenging piece to perform.