Abstract: The text analyzes the basic ecclesiological principles in the dialogue between Orthodoxy and Catholicism: the papal primacy and the conciliarity. The two forms go back in history as far as the Church itself. The author considers them exclusively in the very context of the development following the Second Vatican Council. The study examines the present position of the Catholic Church on the relation between primacy and fellowship, as well as the development possibilities of the Catholic Church in the context of the ecumenical dialogue today. Avoiding to state any “solutions”, the study insists on the necessity of knowledge of the genesis and the significance of the main ecclesial principles and structures.

Keywords: communion, conciliarity, papal primacy, Roman Catholic Church, ecumenism