Integrated access to distributed, heterogeneous information sources is becoming more and more important for organizations, research collaborations, and businesses in order to efficiently manage and leverage existing knowledge. In this book a novel approach for virtual information integration based on Semantic Web technologies is presented. Compared to traditional approaches, the system is able to integrate distributed, heterogeneous data sources based on ontologies. This strategy enables a concept- based approach, where data is described based on its meaning, instead of a functional data model. The presented approach is very flexible, since no explicit global schema needs to be maintained. New data sources are mapped to domain ontologies published on the Web (or intranet) and once they are registered at the system, they can be transparently accessed together with all the other information based on powerful semantic queries. Combined with latest research towards new graphical user interfaces for Linked Data on the Semantic Web, the proposed approach is well suited for large-scale collaborative knowledge sharing in research as well as in the industry.