Mary has a unique and privileged place in salvation history and in the Church. Because she responded yes to becoming the Mother of God, she is our first model of discipleship and our model of grace and trust in God.
The Immaculate Conception is the doctrine that Mary was preserved free from original sin from the first moment of her conception. Prior to the Middle Ages, there was no discussion of this idea. When the idea was suggested, prominent theologians, including Saints Anselm and Thomas Aquinas, opposed it.
Gradually, however, the idea took hold, and the 16th-century Council of Trent excluded Mary when it talked about original sin. On December 8, 1854, Blessed Pope Pius IX defined the Immaculate Conception as a dogma of the Catholic Church. Eight years earlier, the bishops of the United States had chosen Mary under the title of her Immaculate Conception to be patroness of their country. Thirty-one dioceses in the United States have adopted Mary of the Immaculate Conception as their patroness. Today the largest Catholic church in the Americas is the Basilica of the National Shrine of the Immaculate Conception in Washington, D.C.