The collections of printed books were greatly enriched in 1855 by the Cicognara collection, made up of books relating to art and antiquities. Since the end of the nineteenth century, the Borghese manuscripts (1891), the Barberini (1902), Borgiani (1902), Rossiani (1921), Chigi (1923), and Ferrajoli (1926) collections of manuscripts and printed books, the Archive of the Chapter of St. Peter’s (1940), and the Patetta collection (1945), among others, have become part of the Library collections.

Under Leo XIII a modernizing process was initiated by the then Prefect (and later, Cardinal Librarian), Franz Ehrle, S. J., who opened the present reading room for printed books (Sala Leonina); adopted detailed norms for the printed catalogues of manuscripts, which have been applied in a large number of catalogues and which continue to be used today; and established the Library’s Restoration Laboratory.

The cataloguing of printed books was standardized after the First World War with the well-known Norme per il catalogo degli stampati (Norms for cataloguing printed books), which have been reprinted and translated many times.

Recent years have seen the construction of a new, underground depository for the manuscript stacks and of a new Reading Room for Periodicals.