This master's thesis is dedicated to the theological disputation upon the using of the title Theotokos for Virgin Mary that had been finally resolved at the Third Ecumenical Council in Ephesus in 431 AD. The first part deals with the crucial moments of deepening theological knowledge in the Church history in order to show a development of the disputation mainly in the 3rd and 4th century. Although Christology wasn't the main theme of the teachings of the Church in that early period some of the theologians especially Irenaeus, Origen, Paul of Samosata and Apollinaris of Laodicea also raised some issues in the field of Christology. The end of the first part offers an inside into the theological mindset of both sides of the disputation - Diodorus of Tarsus and Theodor of Mopsuestia on the one side and the Orthodox fathers Athanasius, the Cappadocian Fathers, Didymus the Blind and John Chrysostome on the other side. The second part presents the written sources of the disputation and offers an insight to its beginning and development. The third and main part focuses on the correspondence between Cyril of Alexandria and Nestorius mainly on their Second Epistles containing the major topics of the disputation. It discusses a content of these two epistles and also analyses and compares theological arguments of both...

La Déclaration christologique commune signée à Rome en 1994 entre l’Église catholique et l’Église assyrienne témoigne d’une volonté réelle de retour à la foi une et commune entre les deux Églises. Elle met un terme à une séparation datant du Ve siècle, lors des querelles christologiques entre les deux patriarches Nestorius et Cyrille d’Alexandrie. L’Église de l’Orient vit, depuis toujours, un double isolement : l’un géographique, politique et culturel car située jadis en dehors des frontières de l’Empire romain, et l’autre dogmatique et ecclésiologique dû à sa défense de maîtres œcuméniques condamnés tels Nestorius et Théodore de Mopsueste. Elle exploite des termes anthropologiques kyana (nature), qnoma et parsopa (personne), de la langue syriaque, à la base des controverses et des incompréhensions sur la personne une du Christ. Dans ce débat, le rôle de Mar Babaï le Grand, au VIIe siècle, est capital, car il donne, dans son livre Liber de Unione, une définition précise de ces termes et systématise la théologie syro-orientale. Il est à l’origine de la confession christologique : deux natures, deux qnomé en une personne. La Déclaration christologique de 1994, révèle au monde ce qui unit les deux Églises : la personne du Christ. Elle est le fruit d’un travail concerté du Conseil pontifical pour la promotion de l’unité des chrétiens et de l’Église de l’Orient. Le désir de Mar Denkha IV, de signer un accord christologique avec Rome a rencontré celui d’André de Halleux, du côté catholique et de Mar Bawai Soro, du côté assyrien. Le Comité mixte assyro-catholique poursuit cette tâche en vue de l’unité, de 1995 à 2004, épaulé par la Fondation « Pro Oriente ». En 2005, le dialogue est suspendu avec le refus de la signature de l’accord sur les sacrements par les Assyriens. L’année 2007, laisse entrevoir une reprise possible du dialogue entre les deux partis. / The Common Christological Declaration signed in Rome in 1994 between the Catholic Church and the Assyrian Church testifies to a genuine desire for a return to the common faith between the two Churches. It puts an end to a separation dating from the 5th century, due to the Christological quarrels between the two patriarchs Nestorius and Cyril of Alexandria.The Church of the East has always had a double isolation: one geographical, political and cultural since it was formerly outside the borders of the Roman Empire, and the other dogmatic and ecclesiological due to its defense of ecumenical masters condemned such as Nestorius and Theodore de Mopsueste. It exploits the anthropological terms kyana (nature), qnoma and parsopa (person), of the Syriac language, at the basis of the controversies and misunderstandings on the one person in Christ. In this debate, the role of Mar Baba the Great in the seventh century is crucial, for in his book Liber de Unione he gives a precise definition of these terms and systematizes Syro-Oriental theology. He is at the origin of the Christological confession: two natures, two qnome in one person. The Christological Declaration of 1994 reveals to the world what unites the two Churches: the person of Christ. It is the result of a concerted effort by the Pontifical Council for the Promotion of the Unity of Christians and the Church of the East. The desire of Mar Denkha IV to sign achristological agreement with Rome met that of André de Halleux on the Catholic side and Mar Bawai Soro on the Assyrian side. The Assyro-Catholic Joint Committee continued this task with a view to unity, from 1995 to 2004, supported by the "Pro Oriente" Foundation. In 2005, the dialogue was suspended with the refusal of the Assyrians to sign the agreement on the sacraments. The year 2007, aims at resuming the dialogue between the two parties.