Orthodox Christian faith can be succinctly summarized by one of the oldest statements, which is both a prayer and a confession of faith. It is called the Creed, which is also known as the Nicene Creed, or Symbol of Faith.
 I believe in One God, the Father Almighty, Maker of heaven and earth, and of all things visible and invisible.  And in One Lord Jesus Christ, the Son of God, the Only-begotten, begotten of the Father before all ages.  Light of Light, true God of true God, begotten not made, of one essence with the Father, by Whom all things were made.  Who for us and for our salvation came down from heaven, and was incarnate of the Holy Spirit and the Virgin Mary, and became man.  And He was crucified for us under Pontius Pilate, and suffered, and was buried.  And the third day He rose again, according to the Scriptures,  and ascended into heaven, and sits at the right hand of the Father,  and He will come again with glory to judge the living and the dead, Whose Kingdom will have no end.  And in the Holy Spirit, the Lord, the Giver of Life, Who proceeds from the Father, Who with the Father and the Son together is worshipped and glorified, Who spoke by the Prophets.  In One, Holy, Catholic*, and Apostolic Church.  I acknowledge one baptism for the remission of sins.  I look for the resurrection of the dead, and the life of the world to come. Amen.
* Means "full," "complete," "whole," "with nothing lacking," and "universal," "all-encompassing," pertaining to the whole Christian body. This is not a reference to the Roman Catholic church
The word creed comes from the Latin credo which means “I believe.” In the Orthodox Church the Creed is usually called The Symbol of Faith which means literally the “bringing together” and the “expression” or “confession” of the faith.
In the early Church (prior to the Ecumenical Councils) there were many different forms of the Christian confession of faith; many different “creeds.” These creeds were always used originally in relation to baptism. Before being baptized a person had to state what he believed. The earliest Christian creed was probably the simple confession of faith that Jesus is the Christ, that is, the Messiah; and that the Christ is Lord. By publicly confessing this belief, the person could be baptized into Christ, dying and rising with Him into the New Life of the Kingdom of God in the Name of the Father, and of the Son, and of the Holy Spirit.
As time passed different places had different statements faith, all professing the identical faith, yet using different forms and expressions, with different degrees of detail and emphasis. These statements of faith usually became more detailed and elaborate in those areas where questions about the faith had arisen and heresies had developed.
In the 4th century a great controversy developed in Christendom about the nature of the Son of God. Some said that the Son of God is a creature like everything else made by God. Others contended that the Son of God is eternal, divine, and uncreated. Many councils met and made many statements of faith about the nature of the Son of God. The controversy raged throughout the entire Christian world. It was the definition of the council which the Emperor Constantine called in the city of Nicea in the year 325 AD which was ultimately accepted by the Orthodox Church as the proper Symbol of Faith. This council is now called the First Ecumenical Council, and this is what it said: We believe in one God, the Father Almighty, Maker of heaven and earth, and of all things visible and invisible. And in one Lord Jesus Christ, the Son of God, the only-begotten, begotten of the Father before all ages. Light of Light; true God of true God; begotten, not made; of one essence with the Father, by whom all things were made; who for us men and for our salvation came down from heaven, and was incarnate of the Holy Spirit and the Virgin Mary, and became man. And He was crucified for us under Pontius Pilate, and suffered, and was buried. And the third day He rose again, according to the Scriptures; and ascended into heaven, and sits at the right hand of the Father; and He shall come again with glory to judge the living and the dead; whose Kingdom shall have no end.
Following the controversy about the Son of God, and essentially connected with it, was the dispute about the Holy Spirit. The following definition of the Council in Constantinople in 381 AD, which has come to be known as the Second Ecumenical Council, was added to the Nicene statement: And [we believe] in the Holy Spirit, the Lord, the Giver of Life, who proceeds from the Father; who with the Father and the Son together is worshipped and glorified; who spoke by the prophets. In one Holy, Catholic, and Apostolic Church. I acknowledge one baptism for the remission of sins. I look for the resurrection of the dead, and the life of the world to come. Amen.
This whole Symbol of Faith was ultimately adopted throughout the entire Church. It was put into the first person form “I believe” and used for the formal and official confession of faith made by a person (or his sponsor-godparent) at his baptism. It is also used as the formal statement of faith by a non-Orthodox Christian converting to the Orthodox Christian Faith. In the same way the Creed became part of the life of Orthodox Christians and an essential element of the Divine Liturgy of the Orthodox Church at which each person formally and officially accepts and renews his baptism and membership in the Church. Thus, the Symbol of Faith is the only part of the liturgy which is in the first person. All other songs and prayers of the liturgy are plural, beginning with “we”. Only the statement of faith begins with “I.” This is because faith is first personal, and only then corporate and communal.
To be an Orthodox Christian is to affirm the Orthodox Christian Faith. It means as well to affirm all that this statement implies, and all that has been expressly developed from it and built upon it in the history of the Orthodox Church over the centuries down to the present day.