Bach's preludes and fugues for organs have never suffered from neglect. While Bach's vocal works fell into eclipse soon after his death in 1750, his keyboard compositions continued to draw considerable approbation. The preludes and fugues, as part of this esteemed repertoire, remained in wide use throughout the eighteenth and nineteenth centuries. Consequently they number among the best-known and most-frequently discussed works of the baroque era. They were already available in several printed editions by the time the first volume of the BG appeared in 1851. They were treated at some length in the ground-breaking nineteenth-century biographies of Forkel, Hilgenfeldt, Bitter, and Spitta. Since then they have been discussed in general terms in the numerous monographs dealing with the organ repertoire or Bach's organ compositions in particular. Hence it is surprising that no one has singled out the preludes and fugues for a full-scale study, taking into consideration the sources, the style, the chronology, and other equally important aspects of the pieces. The present volume focuses on half of this task, the detailed investigation of the preludes. Included in this study will be all those compositions--called prelude, toccata, fantasia, or otherwise--which fulfill an introductory purpose. Thirty-three works fall into this category: nine single pieces and twenty-four preludes from prelude-fugue pairs.