quality:corruption, structural:reformatting
Organ works

Bach was best known during his lifetime as an organist, organ consultant, and composer of organ works in both the traditional German free genres (such as preludes, fantasias, and toccatas) and stricter forms (such as chorale preludes and fugues). At a young age, he established a reputation for creativity and the ability to integrate foreign styles into his organ works. A decidedly North German influence was exerted by Georg Böhm, with whom Bach came into contact in Lüneburg, and Dieterich Buxtehude, whom the young organist visited in Lübeck in 1704 on an extended leave of absence from his job in Arnstadt. Around this time, Bach copied the works of numerous French and Italian composers to gain insights into their compositional languages and later arranged violin concertos by Vivaldi and others for organ and harpsichord. During his most productive period (1708–1714), he composed about a dozen pairs of preludes and fugues, five toccatas and fugues, and the Orgelbüchlein or "Little Organ Book", an unfinished collection of 46 short chorale preludes that demonstrate compositional techniques in the setting of chorale tunes. After leaving Weimar, Bach wrote less for organ, although some of his best-known works (the six Organ Sonatas, the German Organ Mass in Clavier-Übung III from 1739, and the Great Eighteen Chorale Preludes, revised late in his life) were composed after leaving Weimar. Later in his life, Bach extensively consulted on organ projects, tested new organs, and dedicated playing organs to afternoon recitals. The Canonic Variations on "Vom Himmel hoch da komm' ich her" and the Schübler Chorales are organ works Bach published in the last years of his life.