The European Library

If you're trying to find an obscure or specialist book there are few finer resources than National Libraries, to which publishers are often legally required to send copies of everything they produce. However, because European historians often have to study material published in various countries and languages they often have to search several different national libraries. Well, they did have to, but no more, because 'The European Library' has gathered them all together into one database. As they put it:

"The European Library offers free access to the combined resources of the national libraries of Europe. It offers free searching and delivers digital objects. The European Library was initially set up as an EU project. It is now owned by the Conference of European Librarians, and financially supported by the participating libraries. The service is aimed at informed citizens world-wide (both professional and non-professional) who want a powerful and simple way of finding library materials. Moreover, it is expected to attract researchers as there is a vast collection of high-quality, deep-web material from all disciplines."

Of course, the library covers more than just historiography, but it also covers more than books: listed collections include maps, posters, music and even portraits.