The Holy See prescribes ten solemnities that are called solemnities of precept that are to be observed as holy days of obligation. They are Nativity of the Lord (25 December), Epiphany of the Lord (6 January), Ascension of the Lord (Thursday in the Sixth Week of Easter), and the Body and Blood of Christ (Corpus Christi) (Thursday after Trinity Sunday); Mary, Mother of God (1 January), Assumption of the Blessed Virgin Mary (15 August), and Immaculate Conception of the Blessed Virgin Mary (8 December); St. Joseph, Husband of the BVM (19 March), St. Peter and St. Paul, Apostles (29 June), and All Saints (1 November).
The Holy See allows episcopal conferences to remove the precept from these holy days. Their decision must be sent to the Holy See for review and confirmation. The Holy See asks episcopal conferences to retain at least Christmas Day - Nativity of the Lord (25 December) and one of the solemnities of Our Lady as a solemnity of precept. If the precept is removed from one of the days in honour of the Lord it must be moved to a Sunday: Epiphany to the Sunday between 2 and 8 January, Ascension to 7th Sunday of Easter, Corpus Christi to Sunday after Trinity Sunday.
In England and Wales we have retained Our Lord’s Nativity. The other three solemnities in honour of Our Lord are transferred to the Sundays. We retain Ss. Peter & Paul and All saints but St. Joseph is not a holy day of obligation. Assumption of BVM is a holy day of obligation in England and Wales but Mary, Mother of God and the Immaculate Conception are not.
There is also another provision in England and Wales that our episcopal conference has decreed following the Holy See’s recognitio. If the Assumption of BVM, Ss. Peter & Paul, or All Saints fall on a Monday or Saturday, the solemnity is transferred to the neighbouring Sunday.