Christians of the Eastern Churches call themselves Orthodox. This description comes from the fifth century and has two closely related meanings. The first definition means 'true teaching'. The Orthodox Church believes that it has maintained and handed down the Christian faith from the days of the Apostles free from error and distortion. The second definition, which is closer to the essence of Orthodoxy, means 'true praise': to bless, praise, and glorify God the Father, the Son and the Holy Spirit is the fundamental purpose of the Church.

The Orthodox Church embodies and expresses the rich spiritual treasures of Eastern Christianity. The Gospel of Christ was first preached and the First Christian communities were established in the lands surrounding the Mediterranean Sea. It was in these eastern regions of the old Roman Empire that the Christian faith matured in its struggle against paganism and heresy.

The spirit of Christianity nurtured in the East had a particular flavour. It was distinct, though not necessarily opposed, to that which developed in the Western part of the Roman Empire and subsequent Medieval Kingdoms in the West. While Christianity in the West spread in lands which knew the legal and moral philosophy of Ancient Rome, Eastern Christianity developed in lands which knew the Semitic and Hellenistic cultures. While the West was predominantly concerned with the Passion of Christ and the sin of man, the East emphasized the Resurrection of Christ and the deification of man. Since the Early Church was not monolithic, the two great traditions existed together for more than a thousand years until the Great Schism divided the Christian Church.

The Great schism between the Eastern and the Western Churches (1054) was the culmination of a gradual process of estrangement between the east and west that began in the first centuries of the Christian Era and continued through the Middle Ages. Linguistic and cultural differences, as well as political events, contributed to the estrangement. From the 4th to the 11th century, Constantinople, the centre of Eastern Christianity, was also the capital of the Eastern Roman, or Byzantine, Empire, while Rome, after the barbarian invasions, fell under the influence of the Holy Roman Empire of the West, a political rival. In the West theology remained under the influence of St. Augustine of Hippo (354-430) and gradually lost its immediate contact with the rich theological tradition of the Christian East.

Theological differences could have probably been settled if there were not two different concepts of church authority. The growth of Roman primacy, based on the concept of the apostolic origin of the Church of Rome which claimed not only titular but also jurisdictional authority above other churches, was incompatible with the traditional Orthodox ecclesiology. The Eastern Christians considered all churches as sister churches and understood the primacy of the Roman bishop only as primus inter pares (first among equals) among his brother bishops. For the East, the highest authority in settling doctrinal disputes could by no means be the authority of a single Church or a single bishop but an Ecumenical Council of all sister churches. Today, Roman Catholics and Protestants are heirs to the Western tradition, and the Orthodox are heirs to the Eastern tradition.

Today the Orthodox Church is a family of "autocephalous" (self-governing) churches, with the Ecumenical (universal) Patriarch of Constantinople holding titular or honorary primacy as primus inter pares (the first among equals). The Orthodox Church is not a centralised organization headed by a pontiff. The unity of the Church is rather manifested in common faith and communion in the sacraments and no one but Christ himself is the real head of the Church. The number of autocephalous churches has varied in history. Today there are many: the Church of Constantinople (Istanbul), of Alexandria (Egypt), of Antioch (with headquarters in Damascus, Syria), of Jerusalem, of Russia, of Romania, of Bulgaria, of Serbia and of Georgia. These first nine autocephalous churches are headed by patriarchs. The others, among them the churches of Greece, Cyprus, Poland, Albania and America, are headed by archbishops or metropolitans. These titles are strictly honorary, as all bishops are completely equal in the power granted to them by the Holy Spirit.

There are also "autonomous" churches (retaining a token canonical dependence upon a mother see) in Czech and Slovak republic, Sinai, Crete, Finland, Japan, China and Ukraine. In addition there is also a large Orthodox Diaspora scattered all over the world and administratively divided among various jurisdictions (dependencies of the above mentioned autocephalous churches).

The Orthodox Church today is a treasury of the rich liturgical tradition handed down from the earliest centuries of Christianity. The sense of the sacred, the beauty and grandeur of the Orthodox Divine Liturgy make the presence of heaven on earth live and intensive. Orthodox Christian art and music have a very functional role in the liturgical life. Orthodox icons are not simply beautiful works of art, they enshrine the immeasurable depth of the mystery of Christ's incarnation in defence of which thousands of martyrs sacrificed their lives.