Gregorian might refer to:
An Old Gregorian, (usually abbreviated OG) is a former member of Downside School, situated near Bath, Somerset, in the United Kingdom.
Alumni are so-named because the school was founded and is still run, to an extent, by monks from the adjoining Benedictine monastery of St Gregory the Great which, since 1814, has been established at Downside Abbey; from 1606 it had been established at Douai in Flanders (today northern France).
Gregorian is a German band headed by Frank Peterson that performs Gregorian chant-inspired versions of modern pop and rock songs. The band features both vocal harmony and instrumental accompaniment.
Originally, Gregorian was conceived as a more pop-oriented group in the vein of Enigma. Under this concept, they recorded the 1991 album Sadisfaction, with lead vocals provided by The Sisters of Oz: Susana Espelleta (Peterson's wife at the time) and Birgit Freud. However, this was the only album in that style.
In 1998, Peterson and his team of Jan-Eric Kohrs, Michael Soltau and Carsten Heusmann re-invented the project to perform popular songs in the Gregorian style. The criteria for song selection were strict; in order to be considered, a song needed to be translatable into the 7-tone scale. For each album, songs were carefully chosen in addition to original songs written by Jan-Eric Kohrs, Amelia Brightman and Carsten Heussman. Twelve vocalists - previously acclaimed session and choir singers - were then hired to record the tracks.