Gregorian may refer to:

• The thought or ideology of Pope Gregory I or Pope Gregory VII (also called Gregorianism)
• Things named for Pope Gregory I:
  • Gregorian chant, the central tradition of Western plainchant, a form of monophonic, unaccompanied sacred song of the western Roman Catholic Church
  • Gregorian mass
  • Brotherhood of Saint Gregory, a community of friars within the Anglican Communion. The community's members, known as "Gregorians", include clergy and laymen. Since 1987 there has also been a parallel order of sisters, the Sisters of Saint Gregory
• The Gregorian Reform (Pope Gregory VII), a series of reforms initiated by Pope Gregory VII and the circle he formed in the papal curia, c. 1050–80, which dealt with the moral integrity and independence of the clergy
• Things named for Pope Gregory XIII:
  • Gregorian calendar, internationally the most widely used civil calendar. It is named after Pope Gregory XIII, who introduced it in October 1582
  • Pontifical Gregorian University, Rome
• The Armenian Apostolic Church, sometimes called the Gregorian Church after Saint Gregory the Illuminator
• The Gregorian telescope, named after James Gregory
• Gregorian (band), German band that performs Gregorian chant-inspired versions of modern pop and rock songs
• Gregorian Antiphonary, an early Christian antiphonary, i.e. book of choral music to be sung antiphonally in services; it is associated traditionally with Pope Gregory I
• Gregorian Consortium, a collaborative association of three pontifical universities/institutes in Rome
• Gregorian Sacramentary, a 10th-century illuminated Latin manuscript containing a sacramentary. Since the 16th century it has been in the Vatican Library as Lat. 3806
• Gregorian Tower, a round tower located above the Gallery of Maps, which connects the Villa Belvedere with the Apostolic Palace in Vatican City
• Gregorian (horse)