This thesis examines factors contributing to Bulgaria’s important role and involvement in the creation the Eastern European Orthodox Community under the cultural influence of Byzantine Empire from the middle of ninth century. The study primarily uses original Greek and Latin sources translated either in Old Church Slavonic or in contemporary Bulgarian, Russian, Serbo-Croatian or English. The approach of this thesis places Bulgarian-Byzantine relations in the context of the creation of the Eastern European Orthodox Community, illustrating that adopting and interpreting of Byzantine culture by the Slavic nations is a process of mutual acculturation, with paramount importance for the creation of the European cultural body. The findings indicate that the cultural and political aspirations of the Bulgarian ruling class in the middle of the ninth century combined with the wide Byzantine cultural expansion followed declining Iconoclasm were the main prerequisite factors for the establishment of a Slavonic literature tradition.