In many Western Christian traditions (especially Anglican, Lutheran, Methodist and Roman Catholic), Midnight Mass is the first liturgy of Christmastide that is celebrated on the night of Christmas Eve, traditionally beginning at 12:00 midnight when Christmas Eve gives way to Christmas Day. This popular Christmas custom is a jubilant celebration of the Mass or Service of Worship in honour of the Nativity of Jesus; even many of those Christian denominations that do not regularly employ the world "Mass" uniquely use the term "Midnight Mass" for their Christmas Eve liturgy.
The tradition of a midnight Vigil on the eve of Christmas began in the East, and was observed in the late fourth century in Jerusalem by a Christian woman named Egeria on the night of January 5 (since Christmas was still celebrated on January 6 at the time as the Western date of December 25 had not yet reached the East). The tradition reached the Western world in the year 430 under Pope Sixtus III in the Basilica of St Mary Major.
By the twelfth century, the practice of midnight Mass had become more widespread as all priests had been granted the faculty of celebrating three Masses on Christmas Day (previously reserved to the Pope), provided the three different propers were celebrated at their appropriate times of midnight, dawn and day.
The practice of celebrating Midnight Mass is traditional in the Roman Catholic Church, although many churches now hold their "midnight" Mass at an earlier hour. Since 2009, the Pope has celebrated this Mass at 10:00 pm, and as a result the official liturgical designation of these texts has been Mass during the Night since 2009. However, when the Mass does occur at midnight, it is still commonly called "Midnight Mass".