Revered by millions, the Papacy is an international power that many nations have viewed with suspicion, some have tried to control, and not a few have spied upon. Ranging across two centuries of world history, this study seeks to throw open the Vatican's doors to reveal the startling but little-known world of espionage in a sacred place. Reviewing the Pontificates of ten popes - from Pius VII, Napoleon's nemesis, to Pius XII, maligned by some as Hitler's pope - David Alvarez provides a history of the intelligence operations and covert activities that reached the highest levels of the Vatican. Populated with world leaders, both famous and infamous, and a rogue's gallery of professional spies, fallen priests, and mercenary informants, his work aims to cast a light into the darker corners of papal history and international diplomacy. Alvarez reveals that the Vatican itself occasionally entered this clandestine world through such operations as a network of informants to spy on liberal Catholics or a covert mission to establish an underground church in the Soviet Union. More frequently, however, the Vatican was the target for hostile intelligence services seeking to expose the secrets of the Papacy. During World War I, for example, Pope Benedict XV's personal assistant was a secret German agent. During World War II, Germany, Italy, Russia and the United States sent spies into the Vatican to discover the pope's intentions. Alvarez recounts these operations and more, including the methods by which the Vatican learned about the Holocaust. Based on diplomatic and intelligence records in Britain, France, Italy, Spain, the United States and the Vatican - with the latter including documents sealed after the author had access to them - this work reveals that the Papacy was often hindered by its inability to collect timely and relevant intelligence. Challenging the long-held notion that the pope is the world's best-informed leader, Alvarez illuminates not only the inner workings of the Vatican but also the global events in which it was inextricably involved.