Holy Day of Obligation

Holy day of obligation, in the Roman Catholic Church, is a day, besides a Sunday, on which its members are required by canon law to attend Mass.

In the United States, such days are: The Solemnity of Mary, Mother of God (formerly observed as the Feast of the Circumcision), which falls on January 1; Ascension Thursday, 40 days after Easter; the Feast of the Assumption, August 15; All Saints Day, November 1; the Feast of the Immaculate Conception, December 8; and Christmas, December 25. In many other countries, Immaculate Conception is not considered a holy day of obligation but the Epiphany (January 6) is (in the United States, Epiphany is celebrated on the Sunday after the first Saturday in January).

White vestments are worn at Masses held on all holy days of obligation, even those which fall during a season of the liturgical year when some other color is used.