In square notation:

or regular notation:

Veni Creator Spiritus is a hymn believed to have been written by Rabanus Maurus in the 9th century. It is sung during the liturgical celebration of the feast of Pentecost (at both Terce and Vespers). It is also sung at occasions such as the entrance of Cardinals to the Sistine Chapel, when electing a new pope, as well as at the consecration of bishops, the ordination of priests, when celebrating the sacrament of Confirmation, the dedication of churches, the celebration of synods or councils, the coronation of kings, the profession of members of religious institutes and other similar solemn events. Paul Hindemith concludes his Concerto for Organ and Orchestra with a “Phantasy on ‘Veni Creator Spiritus.'” Maurice Duruflé used the chant tune as the basis for his composition “Prélude, Adagio et Choral varié sur le thème du ‘Veni Creator'”

See a list of other popular chant themes here.

Videos:
Marcel Dupré – Veni Creator – St. Sulpice, Paris
Aart de Kort – Improvisation on Veni Creator – Schnitger organ of the Grote- of St. Michaëlskerk, Zwolle – from a concert on 6 August 2013