This book is a collection of papers addressing the multi-shaped character of knowledge, new studies and applications in the field of ontology and semantic technology. The semantic dimension of information plays an increasingly central role in a networked, knowledge-centred economy and the need to encode information into computer systems has led to a bias towards Knowledge Engineering (KE) solutions as opposed to Knowledge Management (KM). Although the intersection between KE and KM has led to a general improvement of information systems, the overlap between these two fields has tended to eclipse interest in genuine knowledge processes. For this reason, the fourth FOMI workshop was held to coincide with the 10th European Conference of Knowledge Management (ECKM), with the explicit aim of bringing together KR and KM (sub)-communities, providing a platform for discussion of these topics. Subjects covered include: the evolution of ontologies in accordance with the evolution of the domain they are designed for; the study of the notions of functional composition and decomposition; modular ontologies for architecture; ontology infrastructure for electromagnetics; ontology of beliefs; enterprise modelling; the application of ontology-based methodologies and techniques to knowledge management issues; ontologies for standards and domain ontologies for biomedicine.The double focus on methodological and applicative issues represents the main feature of these FOMI 2009 articles. This comprehensive perspective will advance progress towards new frontiers in information systems and knowledge management, where research and development in formal ontology will play a leading role.