The Holy Days of Obligation are the days other than Sundays on which we celebrate the great things God has done for us through Jesus and the saints. On Holy Days of Obligation, Catholics attend Mass.
Six Holy Days of Obligation are celebrated in the United States.
January 1—Mary, Mother of God
Fortieth day after Easter—Ascension
August 15—Assumption of the Blessed Virgin Mary
November 1—All Saints
December 8—Immaculate Conception
December 25—Nativity of Our Lord Jesus Christ