Through the innovative methodological prism of polycentricity and plurality, this collective volume illuminates the rich religious past of Eastern-Central Europe by examining the multifaceted and dynamic relations between its Christianities, considered here as communities of interactions. Following the baptism of Rus’ at the end of the 10th century, religious life in the region tended to centre around Kyiv, while other centres with different significances and profiles developed concurrently. Polycentricity became even more pronounced with the advent of the Reformation, the Counter-Reformation, and the Enlightenment. As a part of global Christianity, the Kyivan Christianities maintained vast connections and navigated a delicate balance between major poles such as Rome and Constantinople.