Orgelbüchlein

thumb|The court chapel at the Schloss Weimar|Schloss in [[Weimar where Bach was court organist. The organ loft is visible at the top of the picture.]] The Orgelbüchlein (Little Organ Book) BWV 599−644 is a set of 46 chorale preludes for organ – one of them is given in two versions – by Johann Sebastian Bach. All but three were written between 1708 and 1717 when Bach served as organist to the ducal court in Weimar; the remainder and a short two-bar fragment came no earlier than 1726, after the composer’s appointment as cantor at the Thomasschule in Leipzig.

Bach's apparent plan was for a collection of 164 settings of chorale tunes sung during the Church year so that each part of the year was represented. However, only 46 of these were completed. The manuscript, which is now in the Staatsbibliothek, leaves a number of tunes as missing or "ghost" pieces. A project to complete the missing chorales called "The Orgelbüchlein Project" has been launched in the 21st century, where the chorales are written in modern styles. This project took nine hours in the first complete performance, giving an idea of the potential scope of Bach's "little" book. The Orgelbüchlein as Bach left it contains about 80 minutes of music which span the liturgical calendar.