The Immaculate Conception is celebrated on December 8th, or on December 9th when the 8th falls on a Sunday, the “supposed” date of Mary’s conception, since 1477, by decision of Sixtus IV. The feast is confirmed by Clement XI in 1708, and in the dogma of 1854, Pius IX defines Mary as the Immaculate Conception, in the design of God.
The formulation “Immaculate Conception” concerns only the conception of Mary herself, not that of Jesus Christ. On the other hand, what the dogma asserts is that, unlike the rest of humanity, Mary never needed purification or conversion.
The proclamation of this dogma by Pope Pius IX in 1854 is the result of a slow evolution in the Catholic Church. The feast of the Conception of the Virgin is celebrated in the East in the eighth century, it arrives in the West around the tenth century and spreads gradually in Europe. A theological debate is established between theologians of different orders. Both are based on the Fathers of the Church who from the first centuries had evoked this belief. The debate develops from the fourteenth century and extends until the eighteenth century with positions increasingly repeated popes, while encouraging the faithful to celebrate the feast of the Immaculate Conception are still refusing to pronounce the dogma. Pius IX, after having consulted all the Catholic bishops (who mark their approval by a very large majority) as well as commissions of theologians, defines this dogma in a solemn way on December 8, 1854, by the bull Ineffabilis Deus.
The feast of the Immaculate Conception is liturgically fixed on December 8th.
If the Orthodox Church celebrates the feast of the Conception of Mary and names Mary “the Immaculate”, it does not recognize however this dogma of the Immaculate Conception, as well as the Protestants or the other Christian Churches.
Many churches around the world are dedicated to the Immaculate Conception. In art, in painting as in sculpture, the Immaculate Conception is the object of an important iconography.