Ontologies provide a common vocabulary of an area and define, with different levels of formality, the meaning of the terms and the relationships between them. Ontological Engineering refers to the set of activities that concern the ontology development process, the ontology life cycle, the methods and methodologies for building ontologies, and the tool suites and languages that support them. During the last decade, increasing attention has been focused on ontologies. Ontologies are now widely used in Knowledge Engineering, Artificial Intelligence and Computer Science; in applications related to areas such as Knowledge Management, Natural Language Processing, e-Commerce, Intelligent Information Integration, Bio-Informatics, Education; and in new emerging fields like the Semantic Web. The book presents the major issues of Ontological Engineering and describes the most outstanding ontologies that are currently available. It covers the practical aspects of selecting and applying methodologies, languages, and tools for building ontologies. Ontological Engineering will be of great value to students and researchers, and to developers who want to integrate ontologies in their information systems.