The Immaculate Conception is a dogma of the Catholic Church maintaining that from the moment when she was conceived in the womb, the Blessed Virgin Mary was kept free of original sin, so that she was from the start filled with the sanctifying grace normally conferred in baptism. It is one of the four dogmas in Roman Catholic Mariology.
The doctrine of the immaculate conception of Mary concerns her mother's conception of her, not Mary's conception of Jesus (the virgin birth of Jesus) nor the perpetual virginity of Mary. Although the belief that Mary was conceived immaculate was widely held since at least Late Antiquity, the doctrine was not dogmatically defined until December 8, 1854, by Pope Pius IX in his papal bull Ineffabilis Deus. It is not formal doctrine in other Christian denominations. The Feast of the Immaculate Conception is observed on December 8 in many Catholic countries as a holy day of obligation or patronal feast, and in some as a national public holiday.