What is the difference between the Roman Catholic and Orthodox Catholic Churches?

What is the difference between the Roman Catholic and Orthodox Catholic Churches?

The Eastern Orthodox faith, whether Greek, Russian, Romanian, or a number of other expressions, is one faith, one Church. Orthodoxy is often characterized as those Christians in communion with the Patriarch of Constantinople, rather than with the Pope of Rome.

The Holy Orthodox Catholic and Apostolic Church and the Roman Catholic Church were one Church for the first millennium of Christianity, so there are many similarities. Common to both are most of the points of the Nicene Creed (http://www.goarch.org/chapel/liturgical_texts/creed):
* belief in the Holy Trinity - Father, Son and Holy Spirit
* the divinity of Jesus Christ
* the Virgin Birth
* the crucifixion and resurrection of Christ
* the ascension of Christ into heaven
* the future return of Christ and the creation of his everlasting kingdom
* eternal life

Similar also are
* the structure of church governance (a hierarchy of of various ranks and responsibilities of bishops, a priesthood, and a donate)Te * the change of communion bread and wine into the body and blood of our Lord Jesus Christ
* baptism in the name of the Father, Son, and Holy Spirit
* liturgical worship forms
* the major sacraments (baptism, marriage, ordination, confession, etc.)
* male-only clergy
* only celibates may become bishops

Beliefs have become different in some areas over the years. The chief differences, and those which precipitated the split between Orthodox Christianity and Roman Catholicism, commonly called the Great Schism of 1054:

Orthodoxy believes
* the Holy Spirit proceeds from the Father (Nicene Creed and John 15:26)
* the patriarchs of the various churches have no ruling bishop over them all, always having been organized by councils/synods of bishops

Roman Catholicism believes
* the Holy Spirit proceeds from the Father and the Son (an addition to the Creed)
* the Pope of Rome is the presiding bishop over all Christianity

Additional post-schism Catholic dogmas, required for Catholics to believe, but that have never been Orthodox dogmas:
* purgatory
* infallibility of the Pope
* the immaculate conception of Mary

There are additional differences in practice that aren't quite dogma:
* Married men may become deacons and priests in the Orthodox Church
* Orthodox fasting practices are more severe
* Orthodoxy uses the Greek Septuagint for Old Testament, and the original Greek for New.
* The Orthodox use leavened bread in the consecration of communion

Blessings.
/Orthodox

The fellow above answered that about as well as anyone could.

Sometimes we discuss the doctrinal/dogmatic differences -- but the most important thing is that Roman Catholics, Orthodox and Coptic Churches all agree on one very important thing: we are all Apostolic succession churches, and therefor the roots and trunk of Christianity.

OPsaltis answered this beautifully, and I second Tatto's voice - we are far more similar than different.

For me, the Orthodox/Catholic Church is one.