The best bet as a starting point for searching German library catalogs. The KVK is an extremely useful "meta-catalog" that allows for simultaneous searching of several library catalogs, among them the union catalogs for Bavaria, North Rhine-Westphalia and Southwest Germany. The list of covered catalogs keeps growing; it now includes Austrian and Swiss libraries, as well as an increasing number of other national catalogs.
Online database of 15th century printed books, produced by the Staatsbibliothek Preussischer Kulturbesitz in Berlin. Supplements the printed edition with additional indexes and draft versions of new descriptions.
National bibliography for 1701 to 1800 of all German-language imprints and publications in other languages published in German-speaking countries. Includes access to all digital copies of most items in bibliography.
Catalog of the Zentralkartei der Autographen (ZKA); currently contains almost 500,000 records for letters kept and cataloged in German archives and libraries, and brief biographical data for letter writers.