The Semantic Web Deployment Working Group has published the Proposed Recommendation of SKOS Simple Knowledge Organization System Reference. SKOS provides a common data model for sharing and linking knowledge organization systems via the Web. SKOS is a vocabulary for expressing the basic structure and content of concept schemes such as thesauri, classification schemes, subject heading schemes, taxonomies, folksonomies, and other similar types of controlled vocabulary. As an application of the Resource Description Framework (RDF), SKOS allows concepts to be composed and published on the World Wide Web, linked with data on the Web and integrated into other concept schemes. Along with this publication of the SKOS Reference Proposed Recommendation the Working Group has published an updated SKOS Primer Working Draft. Comments are welcome through 15 July.