Under Pope Pius XII, there 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 Eastern Orthodox Christians outside the Church of Rome.
A commission was established in 1929 by Pius XI to draw up a schema for an Oriental Catholic canon code, the Commissionem Cardinalitiam pro Studiis Praeparatoriis Codificationis Orientalis. In 1935, the same pope established another commission with the same goal, the Pontificia Commissio ad redigendum Codicem iuris canonici orientalis, to replace the former.
The Eastern Catholic Churches, not unlike the Latin Church before the Code of 1917, had their own ancient laws, which were not codified. Some reforms of Eastern Church laws for the Eastern Churches were done during the pontificate of Pius XII. The new Church canons promulgated by Pius XII for the government of the Eastern Catholic Churches concern 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 Eastern eparchies (equivalent to dioceses) in Canada, Brazil, Iraq, France and the USA. They were legally independent from the jurisdictions of Latin Church bishops in these regions.
Decentralized authority and increased autonomy of the united Churches were goals of the Corpus Iuris Canonici (CIC) reform. In its new constitutions, Eastern Patriarchs were made almost independent from Rome (CIC Orientalis, 1957). The reforms and writings of Pope Pius XII were intended to establish Eastern Catholics as equal parts of the mystical body of Christ, as pronounced in the encyclical Mystici Corporis Christi.
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.