An ecumenical council is a solemn assembly of the world's bishops convened by the Pope to define doctrine, address heresy, or reform discipline. The Catholic Church recognises twenty-one such councils.
**Nicaea I (325)** — Defined the full divinity of Christ against Arianism; produced the Nicene Creed.
**Constantinople I (381)** — Confirmed the divinity of the Holy Spirit; completed the Nicene-Constantinopolitan Creed.
**Ephesus (431)** — Defined Mary as Theotokos (God-bearer) against Nestorianism.
**Chalcedon (451)** — Defined Christ as one Person with two natures (divine and human) against Monophysitism.
**Trent (1545–1563)** — The Counter-Reformation council: defined Scripture and Tradition, justification, the seven sacraments, and reformed the liturgy.
**Vatican I (1869–1870)** — Defined papal infallibility and the primacy of the Roman Pontiff.
**Vatican II (1962–1965)** — Called by Blessed John XXIII; produced sixteen documents on the Church, liturgy, ecumenism, and the Church in the modern world. Its four constitutions — Lumen Gentium, Dei Verbum, Sacrosanctum Concilium, and Gaudium et Spes — remain authoritative.
Councils
The Ecumenical Councils: A Timeline
From Nicaea I (325 AD) to Vatican II (1962–1965): the twenty-one ecumenical councils that shaped Catholic doctrine.