The Requiem, op. 9, by Maurice Duruflé was commissioned in 1947 by the French music publisher Durand and is written in memory of the composer's father. The work is for SATB choir with mezzo-soprano and baritone soloists. It exists in three orchestrations: one for organ alone, one for organ with string orchestra and optional trumpets, harp and timpani, and one for organ and full orchestra. At the time of commission, Duruflé was working on an organ suite using themes from Gregorian chants. He incorporated his sketches for that work into the Requiem, which uses numerous themes from the Gregorian "Mass for the Dead." Nearly all the thematic material in the work comes from chant.