In October 2019, Pope Francis changed the title of the old Vatican Secret Archive (Archivum Secretum Vaticanum) to the Vatican Apostolic Archive. The change was part of an effort to remove misconceptions arising from the term "Secretum," which in Latin means "private" or "separate" rather than "secret." The archives contain millions of documents dating back over 12 centuries, including state papers, correspondence, and account books. It was separated from the Vatican Library in the 17th century. Formerly closed to outsiders, it is now open to researchers. Prominent contents include a letter from Mary Queen of Scots to Pope Sixtus V requesting her life be saved before her 1587 execution.

Excommunication of Martin Luther:

The archive contains the 1521 letter by Pope Leo X banning Martin Luther from the Catholic Church. It also houses trial minutes against the Knights Templar, ordered by Philip IV of France in 1307.

Trial of Galileo and Michelangelo’s Letters:

The archive holds trial notes for Galileo, who was arrested for stating the Earth revolves around the sun. It also contains letters from Michelangelo warning the Pope that his guards hadn’t been paid for three months. Another valuable document is Henry VIII’s request for the annulment of his marriage to Catherine of Aran, signed by 85 clergymen. To preserve these millions of records, the archive uses climate-controlled rooms. Pope Leo XIII established the School of Palaeography to train scholars. The archives include the "Chigiani Rooms" and the "Nobel Floor." In 2018, Pope Francis opened the archives to journalists to debunk depictions in "Angels and Demons." A restoration lab established in 1958 continues to preserve these historical documents through digitization and physical restoration.