The Bibliotheca Philosophica Hermetica brings together manuscripts and printed works in the field of the Hermetic tradition, more specifically the ‘Christian-Hermetic’ tradition. Following the ‘ad fontes’ principle, The Ritman Library tries to collect the earliest examples of works falling within its collecting interest, that is to say: manuscripts or first and early editions, without, however, ignoring subsequent written and printed sources. To date, the library holds more than 23,000 volumes: ca. 4,500 manuscripts and printed books before 1800, ca. 17,000 books (primary and secondary sources) printed after 1900, unique archival collections and a collection of prints and engravings.