These six piano sonatas were written during the composer's London years, after he had collected much valuable experience in Italy. The so-called ''London'' Bach devoted himself intensively to the possibilities afforded by the newly-developed ''HammerflŘgel,'' and frequently performed in public on the instrument. His Sonatas opp. 5 and 17, all much esteemed by Mozart, have many characteristics of the classical piano sonata. The op. 17 collection was first published in 1774, and was already being reprinted in various countries during the composer's lifetime.