The Vatican Secret Archives (Latin: Archivum Secretum Apostolicum Vaticanum), is the central repository for all of the acts promulgated by the Holy See. These archives also contain the state papers, correspondence, papal account books, and many other documents which the church has accumulated over the centuries. In the 17th century, under the orders of Pope Paul V, the Secret Archives were removed from the Vatican Library and remained absolutely closed to Vatican outsiders until the 19th century, fueling rumors of what might be secreted away there.

Access
Almost all organisations with archives have time restrictions on when their documents may be opened to the public, lest any documents have sensitive information that would be damaging if released. The Vatican Archives is no exception. Customarily, documents are made available to the public after a period of 75 years.
In 1883, Pope Leo XIII opened archives dated 1815 or earlier to non-clerical scholars. The first papal historian to make fundamental use of the Secret Archives was Ludwig von Pastor. Since then, the secret archives of subsequent pontificates have been opened as follows:
On February 20, 2002, Pope John Paul II took the extraordinary step of making available, beginning in 2003, some of the documents from the Historical Archives of the Secretariat of State (Second Section), which pertain to the Vatican's relations with Germany during the pontificate (1922-1939) of Pope Pius XI. The Vatican's reason for this action was "to put an end to unjust and thoughtless speculation." However, the files are not yet available for public review.

1924: Pontificates down to Gregory XVI (died 1846)
1966: Pius IX (1846-1878). Note here that the opening of Pius IX's pontificate was planned during the pontificate of Pius XII
1978: Leo XIII (1878-1903)
1985: Pius X (1903-1914) and Benedict XV (1914-1922) Opening of the archives

Agostino Cardinal Ciasca (19 May 1891 - 4 Jul 1893)
Luigi Cardinal Galimberti (25 Jun 1894 - 7 May 1896)
Francesco Cardinal Segna (4 Jul 1896 - 13 Jan 1908)
Francesco Salesio Della Volpe 26 Oct 1908 - 26 Jan 1911)
Francis Aidan Gasquet (28 Nov 1917 - 5 Apr 1929)
Franz Cardinal Ehrle (17 Apr 1929 - 31 Mar 1934)
Giovanni Cardinal Mercati (15 Jun 1936 - 23 Aug 1957)
Eugène-Gabriel-Gervais-Laurent Tisserant (14 Sep 1957 - 27 Mar 1971)
Antonio Cardinal Samore (25 Jan 1974 - 3 Feb 1983)
Alfons Stickler (8 Sep 1983 - 1 Jul 1988)
Antonio María Javierre Ortas (1 Jul 1988 - 24 Jan 1992)
Luigi Cardinal Poggi (9 Apr 1992 - 7 Mar 1998)
Jorge Maria Cardinal Mejia (7 Mar 1998 - 24 Nov 2003)
Jean-Louis Cardinal Tauran (24 Nov 2003 - 1 Sept 2007)
Raffaele Farina (1 Sept 2007 - ) Archivists of the Vatican Secret Archives
Not included in the Secret Archives is archive of the Apostolic Penitentiary contains papal documents and other material that are not made public due to the Seal of the Confessional. Nevertheless the Secret Archives are the main collection.

Further reading

Actes et Documents du Saint Siège relatifs à la Seconde Guerre Mondiale (Acts and Documents of the Holy See relative to the Second World War)
Acta Apostolicae Sedis
Relations between Catholicism and Judaism
Henry Denifle Sub-archivist at the Vatican (1883-1905)
Archive of the Congregation for the Doctrine of the Faith