Ecumenical Councils

Chalcedon, Council of
The Fourth Ecumenical Council, held in 451, from 8 October until 1 November inclusive, at Chalcedon, a city of Bithynia in Asia Minor.
http://www.newadvent.org/cathen/03555a.htm

Constantinople, First Ecumenical Council of
Called in May, 381, by Emperor Theodosius, to provide for a Catholic succession in the patriarchal See of Constantinople, to confirm the Nicene Faith, to reconcile the semi-Arians with the Church, and to put an end to the Macedonian heresy.
http://www.newadvent.org/cathen/04308a.htm

The Council of Chalcedon - 451 A.D.
Introduction to the council and its historical setting, with text of its decisions.
http://www.piar.hu/councils/ecum04.htm

The Council of Ephesus
A set of texts produced by this "robber's council".
http://www.piar.hu/councils/ecum03.htm

The Council of Nicaea
A Protestant view of this first council.
http://bible.crosswalk.com/History/AD/SketchesofChurchHistory/?chapter=01-11

Ephesus, Council of
The third ecumenical council, held in 431.
http://www.newadvent.org/cathen/05491a.htm

First Council of Constantinople - 381
Introduction to the council and its historical setting, with text of its decisions.
http://www.piar.hu/councils/ecum02.htm

First Council of Nicea - 325 AD
Introduction to the council and its historical setting, with text of its decisions.
http://www.piar.hu/councils/ecum01.htm

Medieval Sourcebook: Full Text Sources
First Ecumenical Council of the Catholic Church, held in 325 on the occasion of the heresy of Arius. It defined the Nicene Creed.
http://www.fordham.edu/halsall/sbook2.html#conc2

Nicaea, Second Council of
A council that was called to deal with the heresy of Iconoclasm.
http://www.newadvent.org/cathen/11045a.htm

Second Council of Constantinople - 553 A.D.
Introduction to the council and its historical setting, with text of its decisions.
http://www.piar.hu/councils/ecum05.htm

Second Council of Nicaea - 787
Introduction to the council and its historical setting, with text of its decisions.
http://www.piar.hu/councils/ecum07.htm

The Seven Ecumenical Councils of the Undivided Church
Translation and introduction by Philip Schaff and Henry Wace. Volume XIV: A Select Library of The Nicene and Post-Nicene Fathers of the Christian Church, Second Series. From Christian Classics Ethereal Library.
http://www.ccel.org/ccel/schaff/npnf214.html

Third Council of Constantinople : 680-681 A. D.
Introduction to the council and its historical setting, with text of its decisions.
http://www.piar.hu/councils/ecum06.htm