The beginning of the twenty-first century has provided abundant evidence of the necessity to reexamine the relationship between Catholicism and the modern, global world. This book tries to proceed on this path with a focus on the meaning, legacy, and reception in today's world of the ecclesiology of Vatican II, starting with Gaudium et Spes 'This council exhorts Christians, as citizens of two cities, to strive to discharge their earthly duties conscientiously and in response to the Gospel spirit.’ Catholicism and Citizenship is a call for a rediscovery of the moral and political imagination of Vatican II for the Church and the world of our time.