This raises the theoretical underpinnings of the work and indicates that the same happened with the Bibliographic Heritage Union Catalogue not only just a good approach, but it is essential to sustained effort over the years. The study examines the virtual library from the user viewpoint and the reader and shows how their interests are always aiming to achieve the primary document; therefore the objective of the librarian must always save time for the reader (to get the book you want). It shows how a virtual library can be accessed from the same OPAC to multiple sources of digital information and how as a general purpose search engines can access virtual libraries. He insists that the creation of metadata allows digital objects are available, accessible and visible data sets ever greater thanks to the collection of metadata used by aggregators. It makes reference to digital imaging as a first step to establish virtual libraries and how to move beyond using optical character recognition. Particular emphasis is placed on new mobile devices and how reading is necessary to address the problems of copyright from a technical standpoint as well as legal and the need to uniquely identify each digital object. It also refers to the new rules of resource description and access to them, absolutely essential to the digital environment and how it is necessary that the metadata can be transmitted using other metadata in turn containing all information about the digital object and the digital object itself. It stresses the need to preserve digital resources and to develop digital preservation policies unlike as was done with printed books and, finally, is the next goal of virtual libraries in elaborating ontologies for semantic Web using entities and relationships designed specifically for that purpose.