Held in Constantinople in 381. Under Emperor Theodosius the Great. 150 Bishops were present.
The Macedonian Controversy
Macedonius, somewhat like Arius, was misinterpreting Church's teaching on the Holy Spirit. He taught that the Holy Spirit was not a person ("hypostasis"), but simply a power ("dynamic") of God. Therefore the Spirit was inferior to the Father and the Son. The Council condemned Macedonius' teaching and defined the doctrine of the Holy Trinity. The Council decreed that there was one God in three persons ("hypostases"): Father, Son and Holy Spirit.
The Creed
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."
Defenders of Orthodoxy
St. Gregory of Nazianzus, the Theologian (329-390)
He was a scholar who studied in Athens with St. Basil the Great; became Patriarch of Constantinople (379); presided at the Second Ecumenical Council; a poet and profound thinker. He wrote many poems, hymns essays, and sermons.
St. Gregory of Nyssa (331-396)
Younger brother of St. Basil the Great. He was a theologian who delved deeply into the truths of the Faith.
St. John Chrysostom (345-407)
John was born and educated in Antioch (Syria). He became Patriarch of Constantinople in 398. He is known for his eloquent and straight-forward sermons (Chrysostomos: "the golden-mouthed"); was responsible for the revision of the Divine Liturgy. He died in exile.
Read about the other Ecumenical Councils: