The Clementinum (Klementinum in Czech) is a historic complex of buildings in Prague. Until recently the complex hosted the National, University and Technical libraries, the City Library also being located nearby on Mariánské Náměstí. The Technical library and the Municipal library have moved to the Prague National Technical Library at Technická 6 since 2009. It is currently in use as the National Library of the Czech Republic. The Weather station Clementinum, founded by the jesuits, is the oldest weather observation considered unique in the whole Central Europe.
The National Library was founded in 1781 and from 1782 the Clementinum was a legal deposit library. In 1918 the newly-established Czecho-Slovak state took over the library. Since 1990, it has been the National Library. It contains a collection of Mozartiana, material pertaining to Tycho Brahe and Comenius, as well as historic examples of Czech literature.