This book constitutes the proceedings of the Third Joint International Semantic Technology Conference, JIST 2013, held in Seoul, South Korea, in November 2013. The 32 papers, included four tutorials and 5 workshop papers, in this volume were carefully reviewed and selected from numerous submissions. The contributions are organized in topical sections on semantic Web services, multilingual issues, biomedical applications, ontology construction, semantic reasoning, semantic search and query, ontology mapping, and learning and discovery.