When Gunter Henle founded his Urtext publishing house in 1948, he opened his catalog with our two-volume edition of Mozart's complete piano sonatas; these still bear the publisher's numbers HN 1 and HN 2. The four-digit order numbers HN 9001 and 9002 merely designate the reduced-sized pocket scores of these larger reference editions, and are textually exactly the same. Naturally, both Mozart volumes (large and small) have been revised many times over the years, enabling G. Henle Verlag, unlike other music publishers, to guarantee that they offer a musical text that reflects the most current state of research. Mozart's autograph manuscript survives for many of the sonatas, and for some works the composer lightly revised and enriched his text before printing, which is why the Henle Urtext edition reproduces both versions in such cases. The editor's preface and Critical Commentary provide detailed information about all sources and textual issues.