Berlin State Library

The Berlin State Library (German: Staatsbibliothek zu Berlin) is a national library in Berlin, Germany and a property of the Prussian Cultural Heritage Foundation. It is the largest and most important academic research library in the German speaking world. It collects texts, media and cultural works from all fields in all languages, from all time periods and all countries of the world, which are of interest for academic and research purposes.

More information on the Wikipedia page

The website, in German, is.

See also Berlin Central and Regional Library, Berlin City Library and Berlin Document Center