In his study of Bach's Clavier-Ubung III, Gregory Butler makes a major contribution to organ music and Bach studies by giving to original printed copies of this work the kind of attention normally reserved for manuscripts. He details the work's chronology, production, aim, and even spiritual program, treating the prints as unique documents with discernible variants and readings.The need to examine early printed copies of music is being recognized as an important tool which can reveal as much as the study of early manuscripts. Composers themselves frequently took a major role in the preparation of the engraving.Clavier-Ubung III--arguably the most carefully planned, intellectually conceived, and challenging volume of organ music ever published--is a particularly useful example of Bach's printed works known chiefly from the print itself. The print is richer in information than any of the other original prints of Bach's music, making it a distinctly suitable repertory for the author's innovative treatment. Butler reveals fascinating new information on the genesis and history of the collection's composition, finding, in part, that sections of the work were composed considerably earlier than previously was believed.