This volume emerges from the joint work of a research group on Contact and Discourse within Christianity. Byzantium, the Latin West and the Slavic World that was part of the Leibniz ScienceCampus Mainz/Frankfurt Byzantium between Orient and Occident from 2015 through 2019. The project ended with a conference in May 2019 that featured most of the papers contained in this volume. The aim of the research group was to examine religious contact, transfer and debate among the diverse ramifications of Christianity in Europe and the role that the often forgotten Byzantine empire and its versions of the Christian faith played in these processes. The 2019 conference and consequently this volume reflect specifically on the connection between religious exchange and identity construction in Christian communities over Europe. We ask in what ways various groups came into contact, how knowledge about the religious Other was created, and how it was used in discourse.