This chapter has three main goals. Firstly, it highlights how the societal binomial ‘religion and migration’ is a major driver of socio-cultural change in Western countries. It outlines the missions and challenges of immigrant Christian groups by conducting a brief survey of the growing body of sociological research on religious migration, also drawing on other disciplines besides sociology. The second goal is to sharp the sociological notion of immigrant Christianities, that is, a heuristic tool with which to shed light on the presence of a multiplicity of immigrant Churches and Christian movements belonging to the same foreign national community in a host country. The notion emphasises the growing contacts, encounters, disruptions, and entanglements experienced by immigrant Churches, Christian movements, traditions, and groups. The third goal is to ‘narrate’ the subsequent chapters in this volume about the religious life of Romanian immigrants in the Italian peninsula. The chapters are categorized from the disciplinary point of view and by the subject of study, that is, the specific discipline adopted for the research investigation and the Romanian immigrant Church(es) or Christian movement(s) in Italy analysed.