The Nicene Creed

The first part of the seven articles of the Creed were ratified at the First Ecumenical Council.
Held in Nicea, Asia Minor in 325. Under Emperor Constantine the Great. 318 Bishops were present.
The text reads as follows:

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.

The Second Ecumenical Council
Held in Constantinople in 381. Under Emperor Theodosius the Great. 150 Bishops were present.
The holy fathers of the Council added five articles to the Creed. They read as follows:

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.

(The above is from http://www.goarch.org)

Here is a short history of the Ecumenical Councils of the the Orthodox Church.