This chapter explores the impact of migration on denominational minorities in Western Europe, conceptualizing migration as a sociological “particle accelerator” that intensifies religious pluralization. While Christianity has historically undergone confessional diversification through schisms, reformations, and power dynamics, the Age of Migration has exponentially accelerated this process. Migration introduces dynamic majority-minority shifts, reshaping religious landscapes in ways that challenge traditional structures. Empirical data from Germany illustrates how migration fosters both denominational and ethnic diversification, leading to new ecclesial formations. The study also examines responses from major Christian actors—including the Roman Catholic Church, the World Council of Churches and the Lausanne Movement—to this hyper-pluralization. It concludes with reflections on the implications for ecumenical dialogue, interreligious relations and societal cohesion.