Ad caeli reginam is an encyclical of Pope Pius XII, given at Rome, from St. Peter's, on the feast of the Maternity of the Blessed Virgin Mary, the eleventh day of October, 1954, in the sixteenth year of his Pontificate. The encyclical is an important element of the Mariology of Pope Pius XII. It established the feast Queenship of Mary.
Assumed into heaven, Mary is with Jesus Christ, her divine son. With the encyclical, Pope Pius XII institutes the feast Queenship of Mary. Mary should be called Queen, not only because of her Divine Motherhood of Jesus Christ, her only son,, but also because God has willed her to have an exceptional role in the work of our eternal salvation. The encyclical argues, that Christ, because He redeemed us, is our Lord and king by a special title, so the Blessed Virgin also (is our queen), on account of the unique manner in which she assisted in our redemption, by giving of her own substance, by freely offering Him for us, by her singular desire and petition for, and active interest.
Mary was chosen as Mother of Christ in order that she might become a partner in the redemption of the human race; As Christ, the new Adam must be called a King not merely because He is Son of God, but also because He is our Redeemer, so, analogously, the Most Blessed Virgin is queen not only because she is Mother of God, but also because, as the new Eve, she was associated with the new Adam. 
The Church, as the encyclical, always taught that Mary is far above all other creatures in dignity, and after her Son possesses primacy over all. "You have surpassed every creature," sings St. Sophronius. "What can be more sublime than your joy, O Virgin Mother? What more noble than this grace, which you alone have received from God"? To this St. Germanus adds: "Your honor and dignity surpass the whole of creation; your greatness places you above the angels." And St. John Damascene goes so far as to say: "Limitless is the difference between God's servants and His Mother."  Previous Popes are quoted: Pope Pius IX, "With a heart that is truly a mother's," does she approach the problem of our salvation, and is solicitous for the whole human race; made Queen of heaven and earth by the Lord, exalted above all choirs of angels and saints, and standing at the right hand of her only Son, Jesus Christ our Lord, she intercedes powerfully for us with a mother's prayers, obtains what she seeks, and cannot be refused." Leo XIII, said that an "almost immeasurable" power has been given Mary in the distribution of graces; St. Pius X adds that she fills this office "as by the right of a mother."  Pope Pius admonishes theologians and preachers from straying from the correct course, avoiding two extremes, Marian exaggerations and excessive narrowness of mind.  in, our salvation." 
|Dogmas and Doctrines|
The encyclicals points to some countries of the world, where people are unjustly persecuted for their Christian faith and who are deprived of their divine and human rights to freedom. Reasonable demands and repeated protests have not helped them. “May the powerful Queen of creation, whose radiant glance banishes storms and tempests and brings back cloudless skies, look upon these her innocent and tormented children with eyes of mercy” 
- From the earliest ages of the catholic church a Christian people, whether in time of triumph or more especially in time of crisis, has addressed prayers of petition and hymns of praise and veneration to the Queen of Heaven. And never has that hope wavered which they placed in the Mother of the Divine King, Jesus Christ; nor has that faith ever failed by which we are taught that Mary, the Virgin Mother of God, reigns with a mother's solicitude over the entire world, just as she is crowned in heavenly blessedness with the glory of a Queen. 
- Pope Pius XII, Mariological encyclicals and bulls
- Encyclical Fulgens Corona on the Vatican website
- Encyclical Ad Caeli Reginam on the Vatican website
- Encyclical Deiparae Virginis Mariae on the Vatican Website
- Encyclical Ingruentium Malorum on the Vatican website
- Encyclical Le Pelerinage de Lourdes on the Vatican website
- Encyclical Mystici Corporis Christi on the Vatican website
- Apostolic Constitution Munificentissimus Deus on the Vatican Website
- Acta Apostolicae Sedis. (AAS), Vatican City 1939-1958. Official documents of the Pontificate of Pope Pius XII