A holy day of obligation, and the patronal feast of the United States. The Solemnity of the Immaculate Conception celebrates the Immaculate Conception of the Blessed Virgin Mary, on 8 December, nine months before the feast of the Nativity of Mary on 8 September. It is one of the most important Marian feasts in the liturgical calendar of the Latin Church. 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. By royal decree, it is designated as the day honoring the patroness of Portugal. Since 1953, the Pope visits the Column of the Immaculate Conception in the Piazza di Spagna to offer expiatory prayers commemorating the solemn event. The feast was solemnized as a holy day of obligation on 6 December 1708, by the papal bull Commissi Nobis Divinitus of Pope Clement XI. It is celebrated with Masses, parades, fireworks, processions, food and cultural festivities in honor of the Blessed Virgin Mary in Catholic countries. Wiki link Dates computed from the General Roman Calendar. Text: Wikipedia (CC BY-SA).