The tools used by librarians in their daily work have changed vastly during recent years. Today, hardly any library is equipped exactly as it was only a few years ago. In addition to traditional means like card catalogs and microfiche readers, most libraries now also offer an online public access catalog (OPAC), public PCs equipped with CD-ROM drives, scanners, or public terminals connected to the Internet. An increasing number of libraries are building homepages on the World Wide Web from where users have access to a variety of services without physically entering a library.
Many libraries are in transit from the traditional towards the digital library. We witness a shift from libraries offering information about (electronic and print) information towards providing access to full texts of documents. Not only recent publications, but also many historical library holdings are being digitized (see e.g., Corbin and Coletti, 1995). These electronic collections allow users from everywhere at any time to consult the material without doing any harm to fragile documents.
Despite numerous digitization projects, electronic media by no means are dominant compared to print material. There is still a lot of paper in our libraries, and we expect this to be the case for a long time to come. The paper-based library will co-exist with the digital library for the foreseeable future, because electronic publications are not developing at the expense of print media, but in addition to them.
The notion of library has long expanded beyond the physical building of the library. Our services always included access to sources that are physically located outside the library. Over the course of the years, librarians have collaborated in many ways. Central cataloging, union lists of journals, cooperative collection development and interlibrary loan are only a few examples of resource sharing. Forced by decreasing budgets, many libraries have redefined their acquisitions policy from purchasing documents ``just in case'' to ``just in time'', since no library can afford to purchase every item that might be needed by one user one day. Through collaboration and reciprocal services among libraries, we can provide a much larger range of resources to our users and fulfill their information needs quicker, cheaper, and more completely than one library alone would be able to do.
While projects that aim at helping each other might be seen as a nicety during prosperous years and become a necessity in times of economical restraints, they play an ever more essential role in the electronic environment. James Michael suggested a blueprint for the library without walls that consisted of five elements (Michael, 1994):
This last item, interdependency, is the final step for the ``Global Digital Library'' to become reality. In the electronic environment, even more than in the traditional paper-based world, no library can (or may) store all the documents to which it provides access. Digital libraries are only possible if reliable partners cooperate on a long-term basis. Authors, libraries, publishers, archives - the concept of one player in the electronic publishing sector as a self-sufficient entity has been overcome for good. The digital library indeed brings us closer together than ever.