Written in Latin for students at the Gregorian University in Rome, Bernard Lonergan's 1964 De Deo Trino (The Triune God) examines Christian Theology's conception of the Trinity in two parts. The first part, the pars dogmatic, is here translated into English in an edition that includes the original Latin on facing pages.  The section called Prolegomena follows the dialectical development of Trinitarian doctrine by Christian thinkers from the time of the New Testament to the Council of Nicea (325 AD).  The remainder of the volume consists of five theses outlining the evolution of the principal features of Trinitarian doctrine from the New Testament to the Council of Nicea and on through the Patristic era.The Triune God: Doctrines is complementary to the previously published The Triune God: Systematics.  Together they represent the most massive treatment of the doctrine of the Trinity in recent centuries.  This work of translation ensures that Lonergan's masterpiece, De Deo Trino, will at last be available in its entirety to contemporary readers.