The Catechism of the Catholic Church describes holy days of obligation thus:
On Sundays and other holy days of obligation, the faithful are to avoid engaging in work or activities that hinder the worship owed to God, the joy proper to the Lord’s Day, the performance of the works of mercy, and the necessary relaxation of mind and body.
Family needs or essential social service can rightly excuse from the obligation of Sunday rest.
The faithful should see to it that right permission does not extend to habits prejudicial to religion, family life, and health [CCC 2185].
The Code of Canon Law spells out when the holy days of obligation are on the Church’s universal calendar:
Can. 1246 §1. Sunday, on which by apostolic tradition the paschal mystery is celebrated, must be noted in the universal Church as the primordial holy day of obligation. The following days should also be taken note of:
- the Nativity of our Lord Jesus Christ,
- the Epiphany,
- the Ascension,
- the Body and Blood of Christ,
- Holy Mary the Mother of God,
- her Immaculate Conception,
- her Assumption,
- Saint Joseph,
- Saint Peter and Saint Paul the Apostles,
- and All Saints.
These ten are the exact holy days of duty that are celebrated in Vatican City, but there is variation elsewhere (including in Italy). The purpose is that the Code of Canon customs goes on to state:
Can. 1246 §2. With the prior acceptance of the Apostolic See, moreover, the conference of bishops can suppress some of the holy days of obligation or transfer them to a Sunday.
Thus various countries celebrate different holy days of duty (apart from Sunday, which they all celebrate).
The country with the fewest number of holy days of obligation seems to Hong Kong, which has only one: Christmas.
Canada has two: Christmas and Mary, Mother of God.
The United States, differently, has a fairly robust eight holy days of obligation, though two to three have been transferred to Sundays (depending on where you live).
Here is a complete, up-to-date list of the holy days of obligation in the United States:
- Mary, Mother of God (always celebrated January 1, but if this occurs on a Saturday or a Monday there is no obligation to go to Mass)
- Epiphany (this has been permanently translated to the first Sunday after January 1)
- Ascension (this is celebrated on different days depending on which ecclesiastical province you live in; a few provinces celebrate it on the traditional date, which is the Thursday of the sixth week of Easter, but most provinces in the U.S. have transferred it to the seventh Sunday of Easter.)
- The Body and Blood of Christ (this has been permanently converted to the second Sunday after Pentecost)
- The assumption of Mary (always celebrated August 15, but if this occurs on a Saturday or a Monday there is no obligation to go to Mass)
- All Saints (always celebrated November 1, but if this occurs on a Saturday or a Monday there is no obligation to go to Mass)
- Immaculate Conception of Mary (always celebrated December 8)
- Christmas (always celebrated December 25)
There is one other wrinkle to the holy days of obligation in the United States: the state of Hawaii.
Hawaii is part of the United States, but it is situated in a part of the world where most of the surrounding dioceses belong to the Conference of Bishops of the South Pacific.
As a result, there is a special indult for Hawaii to check its liturgical days in line with the surrounding dioceses. Therefore, since 1992, Hawaii has only had two holy days of obligation (besides Sundays), which are the Immaculate Concept (Dec. 8) and Christmas (Dec. 25).