When Christa Landon presented the first printed version of her edition of Joseph Haydn's piano sonatas, Haydn's sonata oeuvre was still overshadowed by the works of Mozart and Beethoven. Since then, Haydn's sonatas have progressed from the teaching rooms to the concert halls and Landon's edition has played a crucial role in that process. The Haydn anniversary in 2009 is a welcome occasion to thoroughly revise this 'legendary' edition for, over the course of more than forty years, new sources have come to light and questions of authenticity have been resolved, not least because the editorial principles for 18th-century music have changed considerably. The new edition comprises all works of the previous Wiener Urtext edition plus the sonata Hob. XVI:16 edited by Landon, along with the Sonata in F major which was rediscovered in Bozen a few years ago and attributed to Joseph Haydn. The new edition is published in four volumes, the content of each volume being compatible with the volumes of the previous edition. Volume 4 contains the same sonatas as volume 3 of the former Wiener Urtext edition. In the Notes on Interpretation, Robert D. Levin explains important aspects of Haydn's performance practice.