The rare book department looks after all (western) books printed before 1801 and the rare and precious books printed after 1801.
Until 1741 the printed books have been described as part of the general collections of Leiden University Library in a number of printed catalogues.
The Bibliotheca Thysiana on the Rapenburg canal (no. 25) in Leiden was founded by testament in 1653 by the young Dutch jurist Johannes Thysius. It is the only Dutch book collection from the seventeenth century which is housed in the original purpose-built library. The collection contains some 2,500 books and several thousand pamphlets on a great variety of subjects.