At inter-confessional joint prayers, Christians of different denominations meet, among them Catholics and Orthodox. Prayer, which is already practiced today in ecumenical relations, reveals the spiritual connection of Christians, and shows that the spiritual-sacramental heritage that connects Christians is greater than the historical and jurisdictional circumstances that separate them. However, it should be borne in mind that gatherings for common prayer are sometimes not perceived by individual representatives or Christian communities as "common" prayer, but "only" as a prayer "in the same place and at the same time", sometimes with the explanation that it is "not directed towards the same. Such attitudes and statements also come from the Orthodox Church and cause confusion, especially among believers who practice prayer with Christians from other churches. But, except Orthodox backgrounds, such or close attitudes can sometimes be heard. and from some other Christian churches and ecclesial communities. The licentiate thesis seeks to explore both official doctrine and theological views and statements expressing either abstinence or outright rejection of the practice of common interfaith prayer, focusing on the more recently relevant Catholic the Orthodox Church, and their theologians and church authorities. The aim of this research licentiate thesis is to give a scientific methodology a realistic and objective picture of the possibility and nature of "common prayer" in ecumenical dialogue, or at joint prayer meetings where a certain, predetermined form of common worship takes place. The paper will, of course, shed light on what the Catholic Church and its Magisterium allow believers to pray together with other Christians and how Catholic Church documents speak of common prayer. This research licentiate thesis is in gradual realization, and the completion of the entire research is planned in the further course of the development of this scientific work according to the doctoral dissertation. In this sense, this work, especially the statements of ecclesiastical authorities and theologians of the Orthodox Church, will be explored in detail in the further process of writing and developing this licensed work.