The Missa Orbis Factor is Mass XI in the Graduale Romanum and is intended for use on Sundays throughout the year. The name for this Kyrie comes from the text of the trope Orbis factor, rex aeternae.

See a list of other popular chant themes here.

Videos:
Pierre Cochereau – Kyrie XI ‘Orbis Factor’ – Introit, Chant and Sortie
Marcel Dupré – Improvised Double Fugue on Kyrie XI ‘Orbis Factor – Recorded 1957