Recent debates about the definition of national identities in Britain, along with discussions on the secularization of Western societies, have brought to light the importance of a historical approach to the notion of Britishness and religion. This book explores anti-Catholicism in Britain and its Dominions, and forms part of a notable revival over the last decade in the critical historical analysis of anti-Catholicism. It employs transnational and comparative historical approaches throughout, thanks to the exploration of relevant original sources both in the United Kingdom and in Australia and Canada, several of them untapped by other scholars. It applies a 'four nations' approach to British history, thus avoiding an Anglocentric viewpoint.