The Eastern Catholic Churches are autonomous (in Latin, sui iuris) particular Churches in full communion with the Bishop of Rome — the Pope. They preserve the liturgical, theological and devotional traditions of the various Eastern Christian Churches with which they are associated, and between which doctrinal differences exist, in particular between the Eastern Orthodox Church, Oriental Orthodoxy and the Assyrian Church of the East. Eastern Catholics recognize that their faith is not at variance with that of other Eastern Catholics and of Latin Catholics, whom they see as equal members of the same Catholic Church. In particular, they recognize the central role of the Bishop of Rome within the College of Bishops. They hold distinct forms (different both from the Latin forms and from those of other Eastern Catholic Churches) of liturgical worship, sacramental and canonical discipline, terminology, traditional prayers and practices of piety. They preserve the special emphases and illuminations that Eastern Christianity has developed over the centuries, some of which Pope John Paul II illustrated in his apostolic letter Orientale Lumen of 2 May 1995.

Most Eastern Catholic Churches have counterparts in other Eastern Churches, whether Assyrian or Oriental Orthodox, from whom they are separated by a number of theological concerns, or the Eastern Orthodox Churches, from whom they are separated primarily by differences in understanding of the role of the Bishop of Rome within the College of Bishops.

The Eastern Catholic Churches were located historically in Eastern Europe, the Asian Middle East, Northern Africa and India, but are now, because of migration, found also in Western Europe, the Americas and Oceania to the extent of forming full-scale ecclesiastical structures such as eparchies, alongside the Latin dioceses. One country, Eritrea, has only an Eastern Catholic hierarchy, with no Latin structure.

The terms Byzantine Catholics and Greek Catholic are used of those who belong to Churches that use the Byzantine liturgical rite. The terms Oriental Catholic and Eastern Catholic include these, but are broader, since they also cover Catholics who follow the Alexandrian, Antiochian, Armenian and Chaldean liturgical traditions.