The sovereign city-state of Vatican City was established in 1929 by the Lateran Treaty with Fascist Italy. Following the death of Pope Pius XI (Achille Ratti) on 10 February 1939, Pope Pius XII (Eugenio Pacelli) had Vatican City officially pursue a policy of neutrality throughout the Second World War. Although the city of Rome was occupied by Germany from October 1943 and by the Allies from June 1944, Vatican City remained unoccupied throughout the Second World War.
Vatican City had no Jewish population. Due to its function as the centre of the Catholic Church and through its network of nunciatures and Church hierarchies throughout Europe, the Vatican gained information from and influenced events in both the fields of international relations as well as the internal affairs of many states and territories, at times touching upon matters related to the Holocaust.
The Vatican Secret Archives are the central repository of Vatican City. Today, permission is granted to consult the documents in the archives up until the end of the papacy of Pius XI (1922-1939). Some of the departments of the Holy See also maintain separate archives.
The (closed) collections covering the Pontificate of Pius XII (1939-1958) at the Vatican Secret Archives contain documents relating to the history of the Holocaust in all European countries. A selection of documents relating to the Second World War has been published in the 11-volume edition Pierre Blet, et al. (eds.), Actes et Documents du Saint Siège relatifs à la seconde guerre mondiale (Acts and Documents of the Holy See related to the Second World War), 1999, Città del Vaticano, Libreria editrice Vaticana, 1965-1981. All volumes, in pdf files, can be accessed by following this link: http://www.vatican.va/archive/actes/index_fr.htm
EHRI Research (Summary)
EHRI has identified the Secret Vatican Archives as the most significant archival institution to hold sources relevant to Holocaust research. The Secret Vatican Archives hold a group of records on prisoners of war (the fond ufficio informazioni Vaticano, 1939-1947) containing documents of the papacy of Pius XII which is open to the public (http://www.archiviosegretovaticano.va/content/archiviosegretovaticano/en/attivita/ricerca-e-conservazione/progetti/inventariazione/ufficio-informazioni-vaticano--prigionieri-di-guerra--1939-1947-.html).
EHRI has yet to explore the exact number and importance of their holdings. Outside of Vatican City, EHRI has found the United States Holocaust Memorial Museum to be the institution which has so far amassed the most considerable amount of sources from, or pertaining to the Vatican Archive Collections, including the records produced by various Apostolic Nuncios and material from the Polish Embassy to the Vatican. The Italian Central Archives of the State (Archivio Centrale dello Stato) hold records of the Italian embassy to Vatican city and other documents. The British National Archives in Kew hold the files of the British Embassy to Vatican City, the National Archives in Washington, D.C. keep the records of the U.S. Personal Envoy to Pope Pius XII, and the London-based Sikorski Institute holds sources produced by the Polish Government-in-Exile. Furthermore, the Hungarian National Archives in Budapest hold a collection of records from the Hungarian Embassy to the Holy See.