Archive Finder describes over 220,000 collections of primary source material housed in thousands of repositories across the United States, the United Kingdom and Ireland.
Dumbarton Oaks Catalog
Located in the Georgetown section of Washington, D.C., this library has important collections and resources related to Byzantine studies.
A catalog to the holdings of the Harvard University libraries, as well as a database of journal articles and reference entries.
Karlsruhe Virtual Catalog
A sort of European union catalog and a counterpart to the mainly US/Canadian WorldCat database.
OASIS - Archival Finding Aids
OASIS provides centralized access to a small but growing percentage of finding aids for archival and manuscript collections at Harvard.
Regesta Imperii Opac
One of the largest databases for European History from Late Antiquity to the Renaissance (16th century)--over 650.000 entries. Coverage includes titles of all relevant disciplines (archaeology, history, art, literature, music, philosophy, languages, theology etc.), titles from the year 1500 up to today, articles from more than 13.000 periodicals (about 1.300 periodicals are completely, about 7.000 are currently indexed), articles from more than 20.000 anthologies (proceedings, Festschriften, etc.), research possible via thesaurus (geographical, period, subjects), and library evidence for all monographs and periodicals.
RLG Union Catalog
The RLG Bibliographic File contains information about more than 22 million books, periodicals, recordings, scores, archival collections, and other kinds of material held in major U.S. research institutions.
VIA - Visual Resources
The Visual Information Access (VIA) system is a union catalog of visual resources at Harvard and Radcliffe.
There are more than 47 million records in the WorldCat database, whose scope includes everything from Babylonian inscriptions to e-books. This database is used to verify citations of items not found in the HOLLIS Catalog, possibly to find a local holding library, or to provide accurate citations for interlibrary loan requests.