The collected works of J.S. Bach, the Neue Bach-Ausgabe, consists of nearly one hundred volumes of Bach's music and many volumes of critical commentary. The commentaries describe Bach's works and the primary sources used to create the edition. The appearance of the index provides easier access to this immense work, which began publication in 1954 and was completed in 2007. The music is indexed by title and BWV number and the commentaries by author and BWV number.
The Neue Bach Ausgabe has many facsimiles of Bach manuscripts, such as the page from the Brandenburg Concerto No. 5 shown below.
To quickly locate a Bach composition in the collected works, you may use the online edition of the New Grove Dictionary in Oxford Music Online. The biographical article for J.S. Bach has a list of his works organized by form, with references to both the Neue Bach-Ausgabe and the earlier collected editon that was completed in 1900. The list of works gives the title of each composition, the BWV number, and the corresponding volumes and page numbers in both Bach editions.
The collected works of Bach are located in the music stacks under the call numbers M3 .B14 and M3 .B143.