The Fourth Sunday of Advent is December 24 this year. In the past, this has caused some confusion among the faithful regarding their obligations for Mass attendance on December 24 and 25.
The Sunday obligation and the Christmas obligation are two separate obligations that can only be fulfilled by attending two separate Masses:
Fourth Sunday of Advent: Any Masses celebrated after 4:00 p.m. on Saturday, December 23 or before 4:00 p.m. on Sunday, December 24
Nativity of the Lord (Christmas Day): Any Mass celebrated after 4:00 p.m. on Sunday, December 24 or before 4:00 p.m. on Monday, December 25.
In addition, January 1, the Solemnity of Mary, Mother of God, is not a Holy Day of Obligation this year because it falls on a Monday. On Sunday, December 31, we celebrate the Holy Family of Jesus, Mary, and Joseph.
The First Sunday of Advent is December 3. The Christmas Season continues through Monday, January 8, on which we celebrate the Baptism of the Lord. On Sunday, January 7, we celebrate the Epiphany of the Lord.