The international standard for thesaurus structure, ISO 259641:2011 – Thesauri for Information Retrieval, published August 2011, presents an extensive data model more advanced than previous versions. The standard facilitates presenting a knowledge organization system in machine compatible SKOS (simple knowledge organization system) format. The model lays out the concepts and terminology applicable to single thesauri, establishing the important difference between concepts and terms. It provides strategies to go beyond simple hierarchical relationships and related concepts, clarifying the nature of relationships between concepts. The new standard addresses several details in thesaurus construction and use for information retrieval, including compound equivalence and node labels. The updated standard supports concept groups or microthesauri and provides for term notes and file versions. Mapping concepts between thesauri will be covered in Part 2 of the standard.