In the Catholic Church, Holy Days of Obligation are the days on which the faithful are obliged to participate in the Mass in addition to Sunday. They have also abstain from unnecessary works, “which hinder the worship to be rendered to God, the joy proper to the Lord’s day, or the suitable relaxation of mind and body.” (Canon 1247 of the Code of Canon Law).
January 1, the solemnity of Mary, Mother of God
Thursday of the Sixth Week of Easter, the solemnity of the Ascension
August 15, the solemnity of the Assumption of the Blessed Virgin Mary
November 1, the solemnity of All Saints
December 8, the solemnity of the Immaculate Conception
December 25, the solemnity of the Nativity of Our Lord Jesus Christ