On 21 November 1990 the newly-rediscovered autograph manuscript of Mozart's Fantasia and Sonata in C minor, K.475 and 457, was auctioned at Sotheby's of London. It was acquired by a consortium of Austrian national and private institutions for £800,000 and is now housed in the library of the International Stiftung Mozarteum, Salzburg. The reemergence of this autograph is the single most significant recent event to affect Mozart scholarship and allows a reappraisal of the genesis of what is perhaps his most important (and certainly his most substantial) solo piano work. For this reason, a separate chapter has been devoted to it alone.

Prior to the rediscovery of the autograph, the Fantasia and Sonata were known from the following sources surviving from Mozart's time:

1. (1) The so-called ‘dedication copy’, containing the Sonata only, written by a Viennese scribe with some corrections in Mozart's hand. Mozart also wrote the title-page: Sonata/ Per il Pianoforte Solo/ Composta/ per la SigmTeresa de Trattnern/ dal suo umilissimo servo/ Woljgango Amadeo Mozart …, dated 14 October 1784

2. (2) The first edition of the Fantasia and Sonata together, published by Artaria in Vienna towards the end of 1785: Fantaisie et Sonate/ Pour le Forte-Piano/ composées pour/ Madame Therese de Trattnern/ par le Maitre de Chapelle/ W.A. Mozart Oeuvre XI

Although published together during Mozart's lifetime the Fantasia and Sonata were evidently conceived independently: according to Mozart's own thematic catalogue the Fantasia postdated the Sonata by some seven months. The rediscovery of the autograph of the two works confirms this: although bound up together in the early nineteenth century their paper-types and stave spans are quite different.