Library catalogues - collective search engine of 81 Luxembourgish libraries

Find-eR - searches the European Commission libraries collections 

HEIDI - Catalogue for libraries of Heidelberg University

KVK - Karlsruhe Virtual Catalog

Library of Congress

Library of the Court of Justice of the EU

Peace Palace Library

Staatsbibliothek zu Berlin

SWB Online-Katalog - 1200 libraries in Baden-Wuerttemberg, Saxony, Saarland, and Rhineland- Palatinate

UNBISnet - UN Bibliographic Information System

WorldCat - 10,000 libraries worldwide