In recent years, numerous libraries have started making descriptions and even digital reproductions of their manuscript holdings available on the internet. Most of these projects, however, focus on the collection of an individual library or on important or attractive parts of it. The real potential of manuscript databases, however, consists in the facilities they open up for cross-collection access to historical holdings. Thus, the German manuscript database Manuscripta mediaevalia aims at making descriptions of all mediaeval manuscripts held in libraries in Germany and some neighbouring countries accessible, including digital images where available. The CERL portal opens up an even wider perspective in terms of time and space, at it aims to include manuscripts of any date held in European libraries in its meta-search engine. A major benefit of such projects is the possibilities they create for a virtual reconstruction of dispersed mediaeval and early modern collections, as exemplified by the library of Nonantula. Thus, these database contribute to a growing awareness for the cultural importance of grown historical collections and may even prevent future dispersals.