Immediately after receiving his degree from the University of Athens and with the generous support of his late professor and academician Amilkas Alivizatos, John Zizioulas received a scholarship from the World Council of Churches. He went for postgraduate studies at Harvard University, where, after a year of research and upon fulfillment of the required academic conditions, he was awarded a Master of Theology (MTS). After special examinations, he was accepted for the doctoral studies program. During the period of these studies, he had the great privilege of learning from eminent professors, including the great Paul Tillich of Systematic Theology, the late great Orthodox Theologian Georges Florovsky of Patristic Theology, the renowned classical philologist, author of the monumental work “Paideia” and editor of the works of Saint Gregory of Nyssa, Werner Jaeger of Patristic Philology, etc. His apprenticeship with these great teachers had a profound effect on his entire thought and scientific course.

As the topic of his doctoral thesis at Harvard University, John Zizioulas received the Christology of Saint Maximus the Confessor, father of the Church of the 7th century. This subject obliged him to familiarize himself simultaneously with both Systematic and Patristic theology. The thought of this great father of the Church decisively influenced all his theological work since then. Unfortunately, while his doctoral work was nearing completion, he was ordered to interrupt his studies and return to Greece to fulfill his military obligations, because it was impossible to grant him a further suspension for his enlistment in the army. So, he returned to his studies at Harvard University after a two-year break to continue writing his doctoral thesis.