Immaculate Conception. In Christian theology, the Immaculate Conception is the conception of the Virgin Mary free from original sin by virtue of the merits of her son Jesus.
The Catholic Church teaches that God acted upon Mary in the first moment of her conception, keeping her immaculate. The Immaculate Conception is commonly confused with the virgin birth of Jesus, the latter being, rather, the doctrine of the Incarnation.
While many Christians believe in the virgin birth of Jesus, it is principally Roman Catholics, along with various other Christian denominations, who believe in the doctrine of the Immaculate Conception. Although the belief that Mary was sinless, or conceived without original sin, has been widely held since Late Antiquity, the doctrine was not dogmatically defined in the Catholic Church until 1854 when Pope Pius IX, declared ex cathedra, i.e., using papal infallibility, in his papal bull Ineffabilis Deus, the Immaculate Conception to be doctrine.
The Catholic Church celebrates the Solemnity of the Immaculate Conception on December 8; in many Catholic countries, it is a holy day of obligation or patronal feast, and in some a national public holiday. The defined dogma of the Immaculate Conception states: We declare, pronounce, and define that the doctrine which holds that the most Blessed Virgin Mary, in the first instance of her conception, by a singular grace and privilege granted