The Orgelbüchlein ("Little Organ Book") BWV 599−644 is a collection of 46 chorale preludes for organ written by Johann Sebastian Bach.
All but three of them were composed during the period 1708–1717, while Bach was court organist at the ducal court in Weimar.
In 1705–1706 he was granted leave from Arnstadt to study with the organist and composer Dieterich Buxtehude in Lübeck, a pilgrimage he famously made on foot. Blasius' Church in Mühlhausen, before his second appointment at the court in Weimar in 1708 as concertmaster and organist, where he remained until 1717.
During the period before his return to Weimar, Bach had composed a set of 31 chorale preludes: these were discovered independently by Christoph Wolff and Wilhelm Krunbach in the library of Yale University in the mid-1980s and first published as Das Arnstadter Orgelbuch.
These four identities are so closely intertwined that it is hard to know where one leaves off and another begins.
Although there are a few important departures, the chorale preludes of the Orgelbüchlein were composed with a number of common stylistic features, which characterise and distinguish the so-called "Orgelbüchlein style:"The brief descriptions of the chorale preludes are based on the detailed analysis in Williams (2003) and Stinson (1999).
The accompanying motif in the lower three or sometimes four parts is derived from a suspirans in the melodic line, formed of a semiquaver (16th note) rest—a "breath"—followed by three semiquavers and a longer fourth note.
It is less predictable and regular than other settings of the same hymn by Bach or predecessors like Buxtehude, only the second and third lines having any regularity.
The remaining three, along with a short two-bar fragment, were added in 1726 or later, after Bach's appointment as cantor at the Thomasschule in Leipzig.
The collection was originally planned as a set of 164 chorale preludes spanning the whole liturgical year.
They form part of a larger collection of organ music compiled in the 1790s by the organist Johann Gottfried Neumeister (1756–1840) and are now referred to as the Neumeister Chorales BWV 1090–1120.
These chorale preludes are all short, either in variation form or fughettas.