There is no division or separation between the Latin rite and the more than 20 Catholic Eastern Churches. There are, however, many differences and distinctions.
These multiple distinctions give each Church its characteristic identity within the one fold which is the Catholic Church.
The most obvious distinctions are external. Each Church uses a distinct ritual for Mass, the sacraments and sacramentals.
For those Churches where there is a corresponding Orthodox Church (for example, the several Byzantine or Melkite Churches, the Coptic, and the Syro-Malankara), an outsider would be hard-put to distinguish between the two celebrations. One key difference with the Orthodox: The Eastern-rite Catholics mention the Pope in the anaphora, or Eucharistic Prayer.
Compared to the Latin-rite Church, the Eastern-rite Churches differ in their internal organization. This is evident, for example, in the guiding role of the patriarch or major archbishop, the means of selecting bishops, and in some cases the presence of married priests.
None of these differences, however, constitute a separation of faith or of communion with the See of Peter.
Because of this, any Catholic may attend, receive Communion, and fulfill the holy day precept at any Catholic rite.
There is no formal procedure required before attending, but the ancient principle of "When in Rome, do as the Romans do" should be diligently applied. Thus a Latin Catholic who wishes to attend one of these rites should acquaint himself with the basic practices and demands of the rite and adapt himself accordingly. For example, most Eastern rites remain standing for most of the celebration and do not kneel for the consecration; a Latin should respect this tradition. Some rites have stricter fasting rules before receiving Communion, and as far as possible a Latin should follow suit.
DECREE ON THE CATHOLIC CHURCHES OF THE EASTERN RITE
SOLEMNLY PROMULGATED BY HIS HOLINESS POPE PAUL VI
ON NOVEMBER 21, 1964
OF THE SUPREME PONTIFF
JOHN PAUL II
TO THE BISHOPS, CLERGY AND FAITHFUL
TO MARK THE CENTENARY
OF ORIENTALIUM DIGNITAS
OF POPE LEO XIII
May 2, 1995