The technical and economic views on metadata together constitute a framework for an engineering (sub-)discipline that focus on mediating information. Advancing that vision was the main motivation of the First Online Conference on Metadata and Semantics Research (MTSR'05). Concretely, the conference aimed at “bringing together researchers and practitioners that share a common interest in metadata, its representation, its semantics and its diverse applications to Information Systems”. The idea of the present e-book was an outcome of the organization activities of MTSR’05. The emphasis on “semantics” addresses the importance of the languages in which metadata records are created, their adequacy for the functions to be enabled and their modular design to adapt to present and future requirements.