This book offers an introduction to the theological and historical aspects of the papacy, an office and institution that is unique in this world. Throughout its history up to our present time, the Petrine ministry is both fascinating and challenging to people, both inside and outside the Catholic Church. Gerhard Cardinal Müller speaks from a particular and personal viewpoint, including his experience of working closely with the pope every day as Prefect of the Congregation for the Doctrine of the Faith. He addresses, in particular, those dimensions of the papal office which are crucial for understanding more deeply the pope as a visible principle of the church’s unity. 500 years after the Protestant reformation, offers insights into the ecumenical controversies about the papacy throughout the centuries, in their historical context. The book also exposes prejudices and cliches, and points to the authentic foundation of the Petrine ministry.