The problems of simple keyword searching are well known; significant differences arise from trivial variations in search statements. These problems can be alleviated by Knowledge Organization Systems (KOS), such as classifications, gazetteers, lexical databases, ontologies, taxonomies and thesauri. KOS model the underlying semantic structure of a domain for the purposes of general retrieval. They act as semantic road maps and make possible a common orientation by indexers and future users – whether human or machine. Douglas Tudhope leads the research on Knowledge Organization Systems and Services.