For almost three centuries, scholars have debated the credibility of the information provided in the colophon of Codex Parisinus graecus 1115. According to this inscription, the manuscript was copied in the year 1276 from another manuscript dating back to the year 774/5; the archetype originated in the papal library at Rome and contains a partial record of the Greek holdings of the library.

The majority of the texts included in the manuscript come from florilegia related to the ecumenical councils. This volume examines the use of florilegia—anthologies of earlier writings—by these councils. Analysis of the contents of the manuscript provides new information concerning, among other things, the beginning of the Filioque controversy and the use of Iconophile florilegia by the seventh ecumenical council in 787. Also revealed is the archetype's role in the negotiations between Rome and Constantinople that led to the Union of the Churches, proclaimed at the Council of Lyons II in 1274, and the indirect involvement of Thomas Aquinas through his Contra Errores Graecorurn.

This monumental two-volume publication brings together in the original languages and an English translation, all the decrees of all the ecumenical councils from Nicaea I to Vatican II. As such it represents an indispensable reference work for theologians and historians, as well as for anyone interested in the development of Christian thought and doctrine. Indeed, these decrees represent the authoritative distillation of Christian tradition which itself is bound together with scripture "in a close and reciprocal relationship" so that the two "form a single sacred deposit of the word of God, entrusted to the church."

The original text is a reproduction of the brilliant edition by G. Alberigo and others of the decrees Conciliorum Oecumenicorum Decreta, which provides for the first time a reliable critical text for all the ecumenical councils. The English translation faces each page of the original text and is the first rendering into English of all these decrees taken together. The translators have used inclusive language throughout to emphasize the continuity of conciliar documents.

The 2,528 total pages of these two volumes include all the authenticated texts and their English renderings as well as a preface and introduction by the oringinal languages editor, a foreword by the English language editor, a bibliography for each decree, various commentaries and explanatory notes, and ten comprehensive indices.