Some theological background is helpful for an understanding of the Virgin Mary in Catholicism. The principal Marian doctrines that have been dogmatically defined by the Roman Catholic Church are summarized below. Fuller details are to be found in the main articles.

Version of the Theotokos of St. Theodore icon, Russian, 1703Maria is truly the Mother of God (De Fide). The dogma that declared Mary as the Mother of God or Theotokos is the central dogma within Mariology. The Council of Ephesus declared:

Therefore we confess one Christ, one Son, one Lord. According to this understanding of the unconfused union, we confess the holy virgin to be the mother of God because God the Word took flesh and became man and from his very conception united to himself the temple he took from her.
This is the oldest of all dogmas concerning the Blessed Virgin. It is not only essential in Marian Theology but also in the Theology of Christ. For if Mary was not Mother of God, then Jesus was in fact not God.

This oldest dogma has given rise to extended Roman Catholic Mariological views in the 20th century. In Redemptoris Mater, Pope John Paul II commented on the self-referential nature of being the Mother of God, by stating: "To the wonderment of nature you bore your Creator!" and in his 1946 publication Compendium Mariologiae, respected Mariologist Gabriel Roschini explained that Mary did not only participate in the birth of the physical Jesus, but, with conception, she entered with him into a spiritual union. Most Mariologists agree with this position.

Mary was a Virgin before, during and after the birth of Christ (De Fide) This was taught by several writers including Ambrose of Milan, Augustine of Hippo, and the Lateran Synod in the year 649 under Pope Martin I. The Catholic Church interprets virginity as including mental virginity (virginitas mentis), sensual virginity (virginitas sensus), that is freedom from sexual desires and corporal virginity (virginitas corporis). The dogma of the Perpetual Virginity of Mary defines the latter. Mary was always a virgin, even after giving birth to Christ-in fact, Christ's birth sanctified his mother's virginity