グレゴリオ聖歌
Gregorian chant was traditionally sung by choirs of men and boys in churches, or by men and women of religious orders in their chapels. It is the music of the Roman Rite, performed in the Mass and the monastic Office. Although Gregorian chant supplanted or marginalized the other indigenous plainchant traditions of the Christian West to become the official music of the Christian liturgy, Ambrosian chant still continues in use in Milan, and there are musicologists exploring both that and the Mozarabic chant of Christian Spain. Although Gregorian chant is no longer obligatory, the Roman Catholic Church still officially considers it the music most suitable for worship. During the 20th century, Gregorian chant underwent a musicological and popular resurgence.