This book describes methodologies for developing semantic applications. Semantic applications are software applications which explicitly or implicitly use the semantics, i.e. the meaning of a domain terminology, in order to improve usability, correctness, and completeness. An example is semantic search, where synonyms and related terms are used for enriching the results of a simple text-based search. Ontologies, thesauri or controlled vocabularies are the centerpiece of semantic applications. The book includes technological and architectural best practices for corporate use. The authors are experts from industry and academia with experience in developing semantic applications.