This text is one of the most important and yet approachable works produced by Cyril. It was written after the Council of Ephesus (431) to explain his doctrine to an international audience. Cyril argues for the single divine subjectivity of Christ, and describes how it encompasses a full and authentic humanity in Jesus - a human experience that is not overwhelmed by the divine presence, but fostered and enhanced by it. Christology becomes then, for St Cyril, a paradigm for the transfigured and redeemed life of the Christian. There is an introduction to the historical and theological background of the time, of the text and to St Cyril himself.