If you had to put a date on when the collection of the Vatican Library began to come together, it would be sometime in the late thirteenth century. The popes of that century's latter decades undertook the mammoth task of trying to reconstruct a new collection of historical texts after the original archive of the Roman Catholic Church — which, by some accounts, dated to the fourth century — was dispersed for unknown reasons in the early 1200s. Formally speaking, the Vatican Library as it exists today was established in 1475, but that inauguration came thanks to the combining of longstanding collections of Greek, Latin, and Hebrew works. The building that houses those original works and all those that have been added until the present is the building that still stands in Vatican City today, commissioned in the late 1500s.
The current collection at Vatican City includes some 75,000 manuscripts and about 1.1 million printed books. That's certainly not the largest collection in the world (by comparison, the Library of Congress boasts more than 61 million manuscripts and some 32 million books), but some of the holdings are extraordinary, including the Codex Vaticanus, which, while incomplete, is believed to be the oldest known manuscript of the Bible.
Vatican Library was temporarily closed to the public in the summer of 2007, while a rebuilding and restoration process got under way. The scheduled date of completion and reopening is September 2010. If that's close to your travel dates, check to ensure work is on schedule by calling (011) 39 06 6987 9402 from the United States.
Unlike St. Peter's Basilica and the Sistine Chapel, you can't just walk up to the Vatican Library, get in line, and wait your turn for a chance to go inside. Texts that are centuries old are delicate, rare, and fragile, and for those reasons the Vatican imposes strict guidelines about who can gain entry.
In general, the library's own rules state that admission is intended for “qualified researchers and scholars from around the world, particularly professors and researchers from universities and other institutions of higher education, and other learned persons known for their writings and scholarly publications.” Still, undergraduate students are rarely given access, and even graduate students can have a tough time making the cut.
Even those who do gain permission to use to the library for research will not necessarily have the right to simply browse. The library's own rules, for instance, prohibit people who show a need to review printed books from even entering the Manuscripts Reading Room. If you think you have what it takes to fill out a successful application to enter the Vatican Library, then you can call for more information from the United States by dialing (011) 39 06 6987 9402.
Vatican Secret Archives
All of that sounds shrouded enough, but there is yet another layer of preserved information inside Vatican City: the Vatican Secret Archives. Pope Paul V ordered about 35,000 volumes removed from the Vatican Library in the 1600s, and these became known as the Secret Archives. Nobody knows for sure how many volumes are in the Secret Archives, since publication of so much as an index listing them is forbidden.
Today, you can access the Secret Archives for research if you meet the tough criteria set by the Vatican (similar to the criteria for doing research in Vatican Library), and — perhaps more crucially — if you already know about the existence of a specific document that you wish to research. Unless you're a biblical scholar, good luck with that one.