John Henry Newman (1801–1890), lecturer in Oxford, Anglican priest and Roman Catholic cardinal, is the most influential convert of modern British history. Even today, through his masterful defense of his conversion, he still convinces many people to follow his example. This study is the first Protestant monograph on the topic, providing an in-depth discussion of Newman’s arguments. Following a reflection on whether something could be learned from these arguments in a Protestant self-criticism, the book raises the question whether Newman’s Apologia is really sustainable.