The First Ecumenical Council of Nicaea (325) marked a decisive moment in the history of Christianity. Convened by Emperor Constantine, the council addressed the Arian controversy concerning the divinity of the Son, the Meletian schism, the date of Easter, which according to Christian tradition was discussed at Nicaea, and issued twenty canons regulating church life. The resulting Nicene Creed became a cornerstone of Christian doctrine, safeguarding the faith against heresy and shaping the Church’s identity. This study surveys the historical context, theological debates, and disciplinary decisions of the council, highlighting its enduring significance for Christian self-understanding and the unity of the Church across the centuries.