The project presents an interconnected view of the Early Modern religious reforms, the fault lines of which are visible in contemporary debates. In the 17th century, following similar developments in Western and Central Europe, the wind of religious change swept throughout Orthodox Christianity with unparalleled intensity. While a consensus has been reached on the pivotal role of the Reforms of Nikon, named after the controversial Patriarch of Moscow (†1681), its causes and far-reaching consequences remain a matter of debate, fuelled by the emergence of new sources and, at times, polemical reassessments. My first aim is to broaden the scope of research by examining unpublished texts held in repositories from Greece, Italy, the Netherlands, Romania and Russia. Based on this data, read against published materials, I will argue that the reformist thrust covered wider areas and aspects than hitherto assumed, affecting even the Orthodox communities of the Ottoman Empire. Focusing on the vital interplay between the religious and political spheres, I will show that Nikon was part of a larger dynamics of religious reforms promoted by such diverse and disputed figures as the ‘Calvinist’ Patriarch of Constantinople Kyrillos Loukaris (†1638), the ‘Westernizer’ Metropolitan of Kiev Peter Mohyla (†1647) and the ‘Orthodox’ Patriarch of Jerusalem Dositheos (†1707). Given the phenomenon’s multi-layered nature, I propose a model of analysis that highlights the specificities, antagonisms and connections between Muscovite, Ruthenian, Wallachian and Greek reforming currents by combining historical, theological and linguistic research tools. My research compares, contextualizes and transgresses boundaries artificially imposed by nationalistic historiographies, while it tackles key topics in Early Modern religious, institutional and cultural history: confessionalization, factional (political) shaping of the ‘Right Faith’ (seen as cultural system) and tension between tradition and innovation.