The Chromatic Fantasia and Fugue BWV 903 and 903a by Bach is one of his most exciting works. It seems to have been highly appreciated during his lifetime, as it survives in many copies that present some very different versions, especially in the Fantasia. Bach appears to have revised it many times. Since there is no authentic manuscript, one of these divergent versions of the Fantasia has been reproduced in the Appendix of the Henle Urtext edition.