The Council of Nicaea in 325 was a momentous event in the history of both the Christian Church and the Later Roman empire. Summoned by the Christian emperor Constantine, Nicaea came to be remembered as the first ecumenical council which composed the original Nicene Creed still used in modified form in most Christian churches today. The assembled bishops gathered to debate the theological questions raised when the Alexandrian presbyter Arius clashed with his bishop Alexander regarding the precise divinity of the Son of God and the Son’s relationship with the Father. Through the surviving documents from the years surrounding Nicaea we can explore the doctrinal and ecclesiastical tensions which fuelled the so-called ‘Arian’ Controversy which divided Christians across the fourth century and beyond. At the same time, the Council of Nicaea also debated the celebration of Easter and issues of Church discipline, while coming to terms with Christianity’s new prestige symbolised by the presence at the council of emperor Constantine. The documents translated here are of great individual value but presenting them as a collection with introductions and commentary allows a closer re-examination of their significance and disputed chronology and the importance of Nicaea in a crucial formative period for the Christian Roman empire.