The classification of entities in the world is complex because each individual has their own abstraction of reality. Ontologies are conceptual models that explicit knowledge shared by a specific community. Recently, collaboration has become an important part of the ontology development process. Using the Web, we can build formal knowledge collaboratively, through shared specification of concepts, properties and relations. This book presents a software engineering approach to allow the specification of accurate domain ontologies through collaboration, considering ontological foundation and visual knowledge support.