Book excerpt: This book is the first to analyze the impacts of migration and transnationalism on global Catholicism. It explores how migration and transnationalism are producing diverse spaces and encounters that are moulding the Roman Catholic Church as institution and parish, pilgrimage and network, community and people. Bringing together established and emerging scholars of sociology, anthropology, geography, history and theology, it examines migrants’ religious transnationalism, but equally the effects of migration-related-diversity on non-migrant Catholics and the Church itself. This timely edited collection is organised around a series of theoretical frameworks for understanding the intersections of migration and Catholicism, with case studies from 17 different countries and contexts. The extent to which migrants’ religiosity transforms Catholicism, and the negotiations of unity in diversity within the Roman Catholic Church, are key themes throughout. This innovative approach will appeal to scholars of migration, transnationalism, religion, theology, and diversity.