Immaculate Conception

The Feast of the Immaculate Conception celebrates belief in the Immaculate Conception of the Blessed Virgin Mary. It is celebrated on 8 December, nine months before the Nativity of Mary, which is celebrated on 8 September. It is the patronal feast day of the United States and the Republic of the Philippines. It is celebrated by the Roman Catholic Church as well as a few other closely related Christian churches.

The Eastern Christian Church first celebrated a feast of the Conception of the Most Holy and All Pure Mother of God on December 9 perhaps as early as the 5th century in Syria. By the 7th century it was already a widely known feast in the East. In the same century the idea of Mary's spotlessness was adopted by Islam and is included in the Qur'an. However, when the Eastern Church called Mary achrantos (spotless or immaculate), it did not define exactly what this meant. Today the majority of Orthodox Christians would not accept the Scholastic definition of Mary's preservation from original sin before her birth that subsequently evolved in the Western Church after the Great Schism of 1054. After the feast was translated to the Western Church in the eighth century, it began to be celebrated on December 8th. It spread from the Byzantine area of Southern Italy to Normandy during the period of Norman dominance over southern Italy. From there it spread into England, France, Germany, and eventually Rome.
Prior to Pope Pius IX's definition of the Immaculate Conception as a Roman Catholic dogma in 1854, most missals referred to it as the Feast of the Conception of the Blessed Virgin Mary. The festal texts of this period focused more on the action of her conception than on the theological question of her preservation from original sin. A missal published in England in 1806 indicates the same collect for the feast of the Nativity of the Blessed Virgin Mary was used for this feast as well.

The first move towards describing Mary's conception as "immaculate" came in the eleventh century. In the fifteenth century Pope Sixtus IV, while promoting the festival, explicitly tolerated those who promoted it as the Immaculate Conception and those who challenged such a description, a position later endorsed by the Council of Trent.
The proper for the feast of the Conception of the Blessed Virgin Mary in the Medieval Sarum Missal, perhaps the most famous in England, merely addresses the action of her conception.
The collect for the feast reads:
O God, mercifully hear the supplication of thy servants who are assembled together on the Conception of the Virgin Mother of God, may at her intercession be delivered by Thee from dangers which beset us.
In 1854, Pius IX made the infallible statement 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."