By pontifical decree, it is the patronal feast day of Argentina, Brazil, Chile, Italy, Korea, Nicaragua, Paraguay, the Philippines, Spain, the United States, and Uruguay.

Since 1953, the Pope visits the Column of the Immaculate Conception in the Piazza di Spagna to offer expiatory prayers commemorating the solemn event.

[2][3][4] It is celebrated with Masses, parades, fireworks, processions, food and cultural festivities in honor of the Blessed Virgin Mary in Catholic countries.

[5] By the 7th century, the feast was already widely known in the East: on at least two occasions in the Acta of the Third Council of Constantinople (680-681), regarded as ecumenical by both the Catholic and Eastern Orthodox Churches, Mary is called "immaculate" (Achrantos).

[9] According to the papal bull Commissi Nobis Divinitus, dated 6 December 1708, Pope Clement XI mandated the feast as a holy day of obligation which is to be celebrated in future years by the faithful.

[12]Pope Pius IX on 8 December 1854 issued the apostolic constitution Ineffabilis Deus: "The most Blessed Virgin Mary, in the first instant of her conception, by a singular grace and privilege granted by almighty God, in view of the merits of Jesus Christ, the saviour of the human race, was preserved free from all stain of original sin.

[17][18] In the Church of England, the "Conception of the Blessed Virgin Mary" may be observed as a Lesser Festival on 8 December without the religious designation as "sinless", "most pure" or "immaculate".

The solemnity is a registered public holiday in the following sovereign countries and territories: The Church of the Company Fire is a major mass casualty incident that occurred during the celebration of the Feast of the Immaculate Conception in Santiago, Chile; on December 8, 1863.

A combination of organisational negligence, overcrowding, mass panic and a highly flammable indoor environment led to a rapidly spreading fire that consumed the church within one hour.