National and University Library in Zagreb (NSK) has been developing and spreading its scope of activity since it was a small library of an institute until these days when it has become a university and national library. The beginning of the 17th century is also the beginning of the story about this library which has changed its official name a couple of times during the history. The arrival of Jesuits to Croatia and their establishment of gymnasiums with their libraries are of upmost importance to the foundation and development of NSK. They founded a gymnasium with a library on Gradec in 1607 which had its librarian and internal organization. In 1816 and 1837 Regulations about mandatory samples were introduced which resulted in NSK gaining a national significance. Then in 1874 NSK got the “university” part of its name which made it more important and influential in Croatian higher education. It has been more than 400 years since its foundation and during the time NSK has been developing continually. It has become the central library in Croatia and University in Zagreb and major cultural, scientific, educational and public institution of national significance.