Orientalium Ecclesiarum, subtitled the Decree on the Eastern Catholic Churches is one of the Second Vatican Council's 16 magisterial documents. "Orientalium Ecclesiarum" is Latin for "of the Eastern Churches," and is taken from the first line of the decree.
One of the shortest conciliar documents, it was approved on 20 November 1964 by a vote of 2,054 in favour and 64 opposed, and was confirmed by a vote of 2,110 to 39 on 21 November 1964, the day when it was promulgated by Pope Paul VI.
The Eastern Catholic Churches of the Catholic Church utilize liturgies originating in Eastern Christianity, distinguishing them from the majority of Catholic liturgies which are celebrated according to the Latin liturgical rites of the Latin Church. While some of these sui iuris churches use the same liturgical ritual families as other Eastern Catholic churches and Eastern churches not in full communion with Rome, each church retains the right to institute its own canonical norms, liturgical books, and practices for the ritual celebration of the Eucharist, other sacraments, and canonical hours.
Historically, tension between Latin Catholics and those worshipping with Eastern liturgies resulted in the latinization, restriction, or prohibition of Eastern liturgies within the Catholic Church. Since the early 20th century, popes have encouraged the usage of traditional liturgies among Eastern Catholics and delatinization. Further emphasis on Eastern Catholic liturgical practice was made during the Second Vatican Council with the publication of the 1964 Orientalium Ecclesiarum.