Staatsbibliothek zu Berlin, the Berlin State Library, is the largest academic universal library in Germany. Its holdings amount to more than 13 million items. Its special collections comprise, for example, occidental and oriental manuscripts, music autographs, various autographs and estates, maps and historic newspapers.
The Berlin and Brandenburg library union (Kooperativer Bibliotheksverbund Berlin-Brandenburg) operates a metasearch engine that you can use to search several libraries' databases (catalogs) simultaneously. Results are presented in one combined list. You can put together your personal database set.
The German National Library (Deutsche Nationalbibliothek, DNB) exhaustively documents all German and German-language publications from 1913 on. All collected works are permanently archived, catalogued and made available to the public. The DNB's holdings amount to approximately 27.8 million items.
Karlsruher Virtueller Katalog (KVK) is a metasearch engine that you can use to simultaneously search literature in library catalogs and in compilations of books in print the world over. From the result lists you can navigate to the full records in the various catalogs.
The journal database Zeitschriftendatenbank (ZDB) documents titles and holdings information for periodicals (journals, newspapers, etc.). Both print and electronic titles are covered. ZDB contains more than 1.6 million records and more than 12.9 million holdings entries.
WorldCat is the world's largest bibliographical database. WorldCat contains holdings information for approximately 2 billion library assets and connects you with holdings and services of over 10,000 libraries worldwide.