What is the difference between the Eastern Catholic Churches and the Orthodox Church?
The early church (from roughly AD 300 to 600) can be loosely categorized as being composed of two parts: one Western and one Eastern. The Western part is what today is called the “Roman Catholic Church” (this is a popular term that is not precisely correct). The Eastern Churches were not as tightly bound as was the Church of Rome. They developed more as a confederation of churches, working together to ensure that they retained their orthodoxy while keeping their particular forms of worship, style of vestments, and so on.
Following the so-called East-West Schism fo 1054, the Churches of the East retained the name Orthodox (from the Greek meaning “right glory”), while the Church of Rome retained the title Catholic (from the Greek meaning “universal”).
In some cases, parts of various Orthodox Churches grew discontented with their treatment at the hands of other Orthodox or local authorities, and they petitioned Rome for union. The first of these was the Chaldean Church and, later, the Union of Brest (1595), which led to a long period of “Uniatism.” Those Orthodox Churches that returned to communion with the Church of Rome are part of what we now call “Eastern Catholic Churches.” In other cases, there was a strong sense of mission to restore unity with Rome. Other Eastern Catholic Churches have no Orthodox counterpart: the Maronites and the Italo-Albanians.
Liturgically and theologically, the churches that were part of the Orthodox Church are no different from their Orthodox counterparts, with a few exceptions: Eastern Catholic Churches accept the teachings of the Church of Rome that were defined after the Schism of 1054 as being universally binding, although they may express them differently, in keeping with their theological background; in the Liturgy there is a point when the priest commemorates his bishop and, if it is a patriarchal church, his patriarch. At this point, Eastern Catholic Churches commemorate the “Pope of Rome.”
Lets’ take this one step further. The term Byzantine simply refers to those churches that follow the liturgical traditions of Byzantium. This includes all the Orthodox Churches and the Byzantine Eastern Catholic Churches. It does not include the Eastern Orthodox that are, generally, Syriac in tradition, nor does it include those Eastern Catholic Churches that follow the Armenian, Chaldean, Coptic, or Syriac Rites.
Excerpt from Faulk, Edward. 101 Questions and Answers on Eastern Catholic Churches. (Paulist Press: Mahwah, NJ) 2007.