From www.mutopiaproject.org

Schübler Chorales is a name usually given to the Sechs Chorale von verschiedener Art ('Six Chorales of Various Kinds') for organ (BWV 645–650), a collection of six chorale preludes by Johann Sebastian Bach, issued around 1748. The title 'Schübler Chorales' derives from the engraver and publisher Johann Georg Schübler, who is named on the title page. All six of the preludes are for an organ with two manuals and pedal, at least five of them transcribed from movements in Bach's cantatas, mostly chorale cantatas, as follows:
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