Liturgical notes for Advent:

Advent 2025 begins at I Vespers of the 1st Sunday of Advent on the afternoon of November 29 and ends after None on December 24. The liturgical color of the season is violet, save for Gaudete Sunday, on which rose vestments may be worn. At solemn Masses of the season, under the 1954 rubrics, deacon and subdeacon wear folded violet chasubles except on Gaudete Sunday and the vigil of Christmas. Under the 1962 rubrics, deacon and subdeacon wear dalmatic and tunicle, respectively, as usual; the folded chasuble is suppressed. Under the 1954 rubrics, the Sundays of Advent are privileged Sundays. The 1st Sunday is of the 1st order; no feast may take its place. All other Sundays of Advent are of the 2nd order and give way only to doubles of the I class. Under the 1962 rubrics, all Sundays of Advent are of the I class and give way to no feast save the feast of the Immaculate Conception. The Gloria is omitted in all Masses of the season; in the Office, the Te Deum is not recited at Matins on Sundays and ferias. On Sundays in Advent, the Alleluia is sung or said, as is the Credo. Under the 1962 rubrics only, the neo-Gallican Preface of Advent found in some editions of the 1962 Missal may be used where authorized in place of the Preface of the Trinity or Common Preface. Unlike Lent, the ferial days of Advent do not have proper Masses; rather, the Mass of the preceding Sunday is resumed. The Alleluia is omitted and the Credo is not said. Under 1954, ferias of Advent are of simple rite and give way to feasts of semi-double or higher rite. Under 1962, the ferias of Lent through December 16 inclusive are of the III class and give way to feasts of the III class or higher. The days of Advent from 17 December to 23 December inclusive, as well as the Ember Days of Advent, are of the II class under the 1962 rubrics. Under both sets of rubrics, the ferial days of Advent are privileged and must be commemorated at Lauds, all Masses (even conventual Mass), and at Vespers when a feast occurs. It is not permissible under 1954 to say the Mass of a feria in place of a feast as permitted during Lent. From 17 to 23 December inclusive, the proper O Antiphons for each day are used at the Magnificat at Vespers. At Mass, flowers are not permitted on the altar, and the organ may be used only to support the singing, except on Gaudete Sunday and major feasts. The First Thursday, Friday, and Saturday (1962 only) votive Masses are permitted during Advent, provided the liturgical day is not of high enough rank (1954: double of the I or II class; 1962: I or II class) to prohibit them. The 1954 rubrics permit ordinary votive Masses, including the Advent Rorate Mass of Our Lady, on all ferial days of simple rite occurring before December 17. Votive Masses are prohibited under the 1954 rubrics from December 17 to 23 inclusive. Under the 1962 rubrics, ordinary votive Masses are prohibited entirely during Advent; this, in theory, forbids the celebration of the Advent Rorate Mass of Our Lady, although, in practice, it is treated as a III class votive Mass, even though the 1960 rubrics make no mention of it. Technically, Advent wreaths should not be placed in the sanctuary, as they are not officially sanctioned by the Church in the pre-1969 rites and no official blessings for them exist in the Ritual. In practice, in my opinion, this is an area where local custom should prevail. Under 1954, the seasonal orations said at Mass on days of simple and semi-double rite during Advent are Deus qui de beatae of Our Lady and either Ecclesiae tuae for the Church or Deus omnium for the Pope. The seasonal orations are not said under the 1962 rubrics, nor are they said under 1954 on semi-double Sundays on which a feast of double rite is commemorated, or on a Sunday within an octave. At Lauds, schema II of the psalter assigned to the respective day of the week is used on all ferial days of Advent (but not on Sundays or on feasts, where schema I is used at Lauds and the Alleluia is sung at Mass). The Marian antiphon is Alma Redemptoris Mater with the V Angelus and the Advent collect Gratiam from the beginning of Advent until None of the vigil of Christmas inclusive.

(Source: LB236 on Twitter.)