Is Greek Orthodox Catholic?

No. The Greek Orthodox Church is part of the Eastern Orthodox communion and is not in communion with Rome, although Orthodox Christians describe their own Church as 'Orthodox Catholic' in the original sense of catholic — universal.

Do Orthodox believe in purgatory?

Orthodox Christians pray for the departed and believe the prayers of the Church help them, but the Orthodox Church has never dogmatically defined purgatory as the Roman Catholic Church has.

Can a Catholic receive communion in an Orthodox church?

Ordinarily no. Orthodox practice restricts communion to Orthodox Christians who have prepared through prayer, fasting and confession.

Orthodox vs Catholic — The Real Differences Explained

The Orthodox Church and the Roman Catholic Church shared a single communion for the first thousand years of Christianity. The Great Schism of 1054 was the formal rupture of a drift that had been widening for centuries, and the differences that remain are real but often misunderstood.

The papacy

This is the decisive difference. Catholics hold that the Bishop of Rome has universal immediate jurisdiction over the whole Church and, under defined conditions, teaches infallibly. Orthodoxy honours Rome as first in honour among equals — a primacy of witness, not of governance — and locates infallibility in the whole Church as it is expressed in an Ecumenical Council received by the faithful.

The filioque

The original Nicene-Constantinopolitan Creed confesses the Holy Spirit "who proceeds from the Father." The West later added "and the Son" (filioque). Orthodoxy objects both to the theology and to the unilateral alteration of a conciliar creed.

Purgatory and the departed

Catholic teaching defines purgatory as a state of purification with satisfaction for temporal punishment. Orthodoxy prays fervently for the dead and speaks of the soul's journey toward God, but has never dogmatised a purgatorial state or a treasury of merit.

Fasting

Orthodox fasting is considerably stricter and more frequent: most Wednesdays and Fridays, plus four multi-week fasting seasons. The classic Orthodox fast excludes meat, dairy, eggs, fish with backbones, wine and oil, with the discipline relaxed on appointed days.

Icons, liturgy and practice

Orthodox churches use two-dimensional icons; Catholic churches also use statuary.
Orthodox parishes commune infants immediately after baptism and chrismation.
Leavened bread is used in the Orthodox Eucharist, unleavened in the Latin rite.
Married men may be ordained to the priesthood in Orthodoxy; bishops are monastics.
Many Orthodox churches still reckon the feasts on the Julian calendar, so Pascha usually falls on a different Sunday from Western Easter.

Frequently asked

Is Greek Orthodox Catholic?: No. The Greek Orthodox Church is part of the Eastern Orthodox communion and is not in communion with Rome, although Orthodox Christians describe their own Church as 'Orthodox Catholic' in the original sense of catholic — universal.
Do Orthodox believe in purgatory?: Orthodox Christians pray for the departed and believe the prayers of the Church help them, but the Orthodox Church has never dogmatically defined purgatory as the Roman Catholic Church has.
Can a Catholic receive communion in an Orthodox church?: Ordinarily no. Orthodox practice restricts communion to Orthodox Christians who have prepared through prayer, fasting and confession.