The Eastern canonical reforms of Pope Pius XII were the several reforms of Oriental canon law and the Codex Iuris Canonici Orientalis, applying mainly to the Oriental Churches united with the Latin Church in communion with the Roman Pontiff. The Holy See's policy in this area had always two objectives, the pastoral care of approximately ten million Christians united with Rome and the creation of positive ecumenical signals to the two-hundred and fifty million Orthodox Christians outside the Church of Rome.
With his concern for the Eastern Catholic Churches with their combined ten million members, Pope Pius continued the initiatives of his predecessors, especially Pope Leo XIII and Pope Pius XI. These Churches, not unlike the Latin Church before the Code of 1917, had their own ancient laws, which were not codified. The reform of Oriental Church laws, the CIC Orientalis for the Oriental Churches, was completed during the pontificate of Pius XII. The new, very comprehensive Church laws governed matrimonial law, Church trials, administration of Church properties and religious orders and individual rights.
After World War II, a new situation developed, as millions of united Christians from Eastern Europe, emigrated to the Western hemisphere: United States, Western Europe, Canada, South America, the Middle East and Australia. The new Church law was welcomed, yet in some points, it was critiqued, for not fully adopting to these new Western circumstances. Traditional Orientals insisted on legal exemptions, allowing them to keep most of the ancient customs and laws. Pastorally, the Pope tried to meet this challenge, by creating independent new oriental eparchies (equivalent to dioceses) in Canada, Brazil, Iraq, France and the USA. They were legally independent from the jurisdiction of Roman Catholic bishops in these regions.
Decentralized authority and increased the independence of the united Churches were aimed at in the Corpus Iuris Canonici (CIC) reform. In its new constitutions, Eastern Patriarchs were made almost independent from Rome (CIC Orientalis, 1957) These reforms and writings of Pope Pius XII were intended to establish Eastern Orientals as equal parts of the mystical body of Christ, as pronounced in the encyclical Mystici Corporis Christi.
Several encyclicals addressed non-legal issues of the Oriental Churches. Orientalis Ecclesiae was issued in 1944 on the 15th centenary of the death of Cyril of Alexandria, a saint common to Orthodox and Latin Churches. Pius XII asks for prayer for better understanding and unification of the Churches. Orientales omnes Ecclesias, issued in 1945 on the 350th anniversary of the reunion, is a call to continued unity of the Ruthenian Greek Catholic Church, threatened in its very existence by the authorities of the Soviet Union. The persecutions of the Church and a foreseeable schism are specifically mentioned and deplored. Sempiternus Rex was issued in 1951 on the 1500th anniversary of the Ecumenical Council of Chalcedon. It included a call to oriental communities adhering to monophysitism to return to the Catholic Church. Orientales Ecclesias was issued in 1952 and addressed to the Oriental Churches, protesting the continued Stalinist persecution of the Church in all Eastern Nations and the Balkans, asking for prayers. Several Apostolic Letters were sent to the bishops in the East. On 13 May 1956, Pius XII addressed all bishops of the Eastern Rite. Mary, the mother of God was the subject of encyclical letters to the people of Russia in Fulgens corona and a papal letter to the people of Russia.
These individual canon law reforms of Pope Pius XII were revised in 1991. The Code of Canons of the Eastern Churches for members of the Eastern Catholic Churches were promulgated on 18 October 1990 by Pope John Paul II and came into effect on 1 October 1991.