For extensive research in addition to Primo there are several other relevant catalogues at regional and national level.
KOBV: The Cooperative Library Network Berlin-Brandenburg is a meta search engine. Here you can search several Berlin and Brandenburg library catalogues at the same time. The KOBV portal thus allows you to find out which library in the region contains a book. The KOBV can be used to order interlibrary loan media that are not available in the libraries of the Freie Universität Berlin.
KVK: The Karlsruhe Virtual Catalog is also a meta search engine indexing library and bookstore catalogues worldwide. From the list of results, you'll get redirected to the information stored in the respective catalog.
ZDB (choose English in the top bar): The Periodicals Database lists the titles and possessions of serial compilations (e.g. journals, newspapers) of serial publications. In addition to the records of printed works, electronic titles are also listed.
EZB (German only): The Electronic Journals Library is the portal for online journals. Under “Bibliothek auswählen” you can find information about the stock of e-journals of other libraries in Germany, Austria, Switzerland, Czech Republic and Slovakia.