This book examines Johannes Herbinius’ Religiosæ Kijovienses Cryptæ (1675) and focuses on three historical contexts: Confessional tolerance in the Polish-Lithuanian Commonwealth, the transfer of knowledge in early modern Europe, and the emergence of Ruthenian national and confessional identity. The study is situated at the intersection of ecclesiastical and interconfessional history, as well as social, political, and intellectual history. It also touches on crucial aspects of comparative theology, regional studies, and cultural anthropology.