The Orthodox Church
The Orthodox Church is the first Christian Church, founded by the Lord Jesus Christ. Her history can be traced in unbroken continuity back to the original Pentecost, the descent of the Holy Spirit on the Apostles. The Orthodox Church has continued in her undiminished and unaltered faith and practice. Today her apostolic doctrine, worship and structure remain intact. For the first 1000 years of Christian history there was 'One Holy Catholic and Apostolic Church'. The word Catholic means 'Universal'. In other words, the Church holds the same beliefs everywhere. The word Orthodox means 'right belief' and was used to distinguish the true faith from heresies that arose in the early Church.
In 1054 a split occurred. The 'Great Schism' when the Roman Catholic Church, under the pope, separated itself from the Orthodox Church with the 'philioque' addition to the Creed. After the Great Schism various other changes in doctrine and practice were made on the part of the Catholic Church which further widened the gap between the two Churches. The Protestant Reformation then scattered the faithful even more, dividing Christians into numerous other denominations.
Today the Orthodox Church is a single, unified body comprised of several autocephalos (self-governing) churches (e.g., Greek Orthodox, Russian Orthodox, etc.). It is held together not by a universal head, but by the double bond of unity in the faith and communion in the sacraments. These autocephalos churches are in full agreement on all matters of doctrine, and between these exclusively is full sacramental communion.