These preludes are grouped in 3 sets of 6 each. The first group comes from the Wilhelm Friedemann Bach Notebook, compiled by J.S. Bach for his eldest son. The second group, which has been preserved in copies made by his pupils, was probably composed by Johann Sebastian. The third group comes from the collection of Johann Peter Kellner, of which only Nos 5 & 6 were undoubtedly written by Johann Sebastian.