This book presents the OntoTag annotation model, which is suitable for both Linguistics and the Semantic Web. OntoTag was conceived when (1) no real standard for linguistic annotation had been released yet, (2) the topic ‘What is an ontology?’ was still under discussion (e.g. AAAI’2002 workshops), (3) no linguistic ontology had been developed yet, (4) the first W3C recommendations about RDF and OWL were under development, and (5) the Semantic Web was, hence, quite a utopia. However, already by that time, this annotation model used all these emergent technologies to [A] merge and link annotations, and also [B] make linguistic tools and resources interoperate. These two goals are achieved in the model by means of its set of linguistic ontologies, which are described in this book as well. OntoTag provides also a methodology and a set of best practices for the annotation of texts, conforming to the guidelines, recommendations and standards published hitherto for annotation in Linguistics and in the Semantic Web. This book presents also OntoTagger, the application that was implemented in order to evaluate the OntoTag model, together with the results obtained from this evaluation.