CRL collects rarely-held research materials; Northwestern is a member and thus NU patrons may borrow microfilm sets or consult microfilm at CRL in Chicago.
Système Universitaire de Documentation, the union catalogue of French university libraries & documentation centers. Contains more than 9 million bibliographic resources.
The world's most comprehensive catalog of library holdings, particularly (though not exclusively) from North American libraries, containing over 2,000,000,000 records from over 10,000 libraries.