When is Immaculate Conception 2027?

The Feast of the Immaculate Conception, on 8 December, celebrates the Catholic doctrine that the Virgin Mary was conceived without original sin. This doctrine — known as the Immaculate Conception — was formally defined as a dogma of the Catholic Church by Pope Pius IX in his papal bull Ineffabilis Deus on 8 December 1854. It is distinct from the Virgin Birth of Jesus; it refers to Mary's own conception in the womb of her mother, Saint Anne.

The feast has been observed in the Western church since the 7th century, though the theological question of whether Mary was conceived without sin was debated for centuries — with Thomas Aquinas among those who questioned it and Duns Scotus among its defenders. The 1854 definition resolved the question definitively for Catholics.

The Immaculate Conception is the patronal feast of several countries. The United States placed itself under the patronage of the Immaculate Conception in 1847, and the Basilica of the National Shrine of the Immaculate Conception in Washington, D.C. is the largest Catholic church in the United States. The day is a public holiday in Spain, Portugal, Italy, Austria, and many Latin American countries.