Chopin's four Impromptus originated in 1834-35 (Op. posth. 66), 1837 (Op. 29), 1840 (Op. 36) and 1843 (Op. 51). Their sources are quite numerous, comprising, as was usual for Chopin, not only parallel French, German and English editions, but also autograph manuscripts, copies and annotated scores belonging to former pupils which reveal refinements to chord spacing and articulation that arose in the course of Chopin's teaching.The Complete Chopin – A New Critical Edition series is recognised as the definitive scholarly edition of Chopin’s music. Under the direction of editor-in-chief John Rink, a team of some of the world’s most respected Chopin specialists contribute their unrivalled collective knowledge to imbue the project with unique authority, drawing upon the latest international scholarship. The Complete Chopin prioritises the needs of the practical pianist and provides a text of each work based on a single principal source together with important variants from other authoritative sources, along with thorough critical commentaries and prefatory essays in English, French and German.