In their theological and historical interactions, neo-Calvinism and Roman Catholicism have often met in moments of conflict and co-operation. The neo-Calvinist statesman Abraham Kuyper polemicized against the Roman Catholic Church and its theology, whilst building bridges between those traditions by forging novel political coalitions across ecclesiastical boundaries. In theology, Gerrit C. Berkouwer, a neo-Calvinist critic of Roman Catholicism in the 1930s, later attended the Second Vatican Council as an appreciative Protestant observer. Telling their stories and others—including new research on lesser-known figures and neglected topics—this book presents the first scholarly volume on those dynamics of polemics and partnership.