What is the Immaculate Conception?

The Immaculate Conception is the Catholic dogma that the Virgin Mary was preserved from original sin from the very first moment of her conception, by a singular grace and privilege of God, in view of the merits of Jesus Christ her Son.

Pope Pius IX solemnly defined this dogma on December 8, 1854, in the apostolic constitution Ineffabilis Deus, declaring it a divinely revealed truth that must be held by all the faithful.