In , theologian James T. O’Connor clarifies the idea of infallibility. He provides a helpful translation of the “relatio” or official explanation by Bishop Gasser given at Vatican I, the Church council that defined the dogma of papal infallibility. Also included in this important volume is the first draft of chapter 4 of the , as well as the final, official chapter of the constitution. Despite its importance in all theological discussions on the doctrine of infallibility, Bishop Gasser’s relatio had never until recently been translated from the Latin original into English. The relatio reveals a mind which is logical in process and fully acquainted with the historical and theological aspects of the question. This volume concludes with a recently updated theological summary on the topic of infallibility by Father O’Connor. is immensely important for theologians and others who wish to understand the way by which the Holy Spirit safeguards the Church. It will be of great value to the general student as well as to the specialist.