A Solemnity of the Roman Catholic Church is a principal holy day in the liturgical calendar, usually commemorating an event in the life of Jesus, his mother Mary, or other important saints. The observance begins with the vigil on the evening before the actual date of the feast.
The word is taken from the Latin sollemnitas, a term of uncertain origin but possibly derived from sollus (whole) and annus (year), indicating a celebration occurring at yearly intervals. The Church always celebrates each solemnity every year.
Solemnities of the Liturgical Year
The following solemnities are observed by the entire Catholic Church.
|Date||Solemnity||Notes about date|
|1 January||Solemnity of Mary, Mother of God||Octave of Christmas|
|6 January||Epiphany of the Lord||If not a Holy Day of Obligation, falls on the Sunday between 2 January and 8 January|
|19 March||Saint Joseph, husband of the Blessed Virgin Mary||Transferred to 20 March if it falls on a Sunday, but to the 18 March if it falls on Palm Sunday or during Holy Week; Episcopal Conferences may transfer it to a date outside of Lent|
|25 March||Annunciation of the Lord||Transferred to 26 March if it falls on a Sunday, but to the Monday after the Second Sunday of Easter if it falls on Palm Sunday, during Holy Week, or during the Octave of Easter|
|First Sunday after the first full moon after the vernal equinox, conventionally taken to be 21 March (22 March to 25 April)||Easter|
|Thursday after the Sixth Sunday of Easter (40th day of Eastertide - 30 April to 3 June)||Ascension of the Lord||If not a Holy Day of Obligation, falls on the Seventh Sunday of Easter (3 May to 6 June)|
|50th day of Eastertide (10 May to 13 June)||Pentecost||A Sunday|
|Sunday after Pentecost (17 May to 20 June)||Trinity Sunday|
|Thursday after Trinity Sunday (21 May to 24 June)||Body and Blood of Christ ("Corpus Christi")||If not a Holy Day of Obligation, falls on the following Sunday (24 May to 27 June)|
|Friday, 8 days after Corpus Christi Thursday, 5 days after Corpus Christi Sunday) (29 May to 2 July)||Sacred Heart of Jesus|
|24 June||Nativity of St. John the Baptist||Transferred to 25 June if a solemnity of the Lord (Corpus Christi or the Most Sacred Heart of Jesus) falls on 24 June|
|29 June||Saints Peter and Paul||Transferred to 30 June if a solemnity of the Lord (Most Sacred Heart of Jesus) falls on 29 June|
|15 August||Assumption of Mary|
|1 November||All Saints|
|Last Sunday before Advent (20-26 November)||Feast of Christ the King|
|8 December||Immaculate Conception of the Blessed Virgin Mary||Transferred to 9 December if 8 December falls on Sunday|
|25 December||Nativity of the Lord (Christmas)|
There are also special solemnities, which are observed in particular places, regions, or in particular religious orders. For instance, when a parish or other church celebrates the feast or memorial of its titular saint or when it celebrates the anniversary of its dedication, it is treated as a solemnity. The feast of Saint Patrick on 17 March is a solemnity in Ireland, and the feast of Our Lady of Mount Carmel on 16 July is a solemnity for the Carmelites.
Some solemnities are also Holy Days of Obligation, on which Catholics are required to attend Mass; some are not. Moreover, the canon law of the Catholic Church requires that on Holy Days of Obligation Catholics are to avoid "work" and "affairs" that "hinder the worship to be rendered to God" or interfere with "suitable relaxation of mind and body" just as is required on Sundays.
Solemnities never impede the Easter Triduum, Pentecost, Sundays of Advent, Sundays of Lent, Sundays of the Easter Season, Ash Wednesday, Holy Week, and the Easter Octave. No solemnity except the Resurrection of the Lord on Easter Sunday can fall during Holy Week or during the Octave of Easter; the Church transfers any otherwise scheduled solemnity to another available date.
Solemnities of the Lord (Epiphany, Annunciation, Ascension, Corpus Christi, Trinity, Christ the King, Nativity), Solemnities of the Blessed Virgin Mary (Mother of God, Assumption, Immaculate Conception), Solemnities of Saints Listed in the General Calendar (Joseph, Nativity of John the Baptist, Peter and Paul, All Saints), All Souls Day, and proper solemnities can impede other Sundays throughout the year.
For all intents and purposes, this means that a solemnity always can impede a Sunday in Ordinary Time.
The Creed is recited at Mass, and there are two scriptural readings and a responsoral psalm before the Gospel. When a solemnity falls on a Friday, the obligation to abstain from meat or do penance is lifted. 
- Liturgical year
- Holy Day of Obligation
- Octave (liturgical)
- Great Feasts of the Orthodox Church
- See General Norms for the Liturgical Year and the Calendar § 59(I)(4).
- Can. 1247, Code of Canon Law
- Codex Iuris Canonici canon 1251.
- Universalis An excellent liturgical calendar of the Catholic Church including the liturgy of the hours and the mass readings.
- "Solemnity" article from The Catholic Encyclopedia (1912)
-  Liturgical calendar for the year 2008 in the United States of America