The Semantic Web Deployment Working Group invites implementation of the Candidate Recommendation of SKOS Simple Knowledge Organization System Reference. This document defines the Simple Knowledge Organization System (SKOS), a common data model for sharing and linking knowledge organization systems via the Web. SKOS provides a model for expressing the basic structure and content of concept schemes such as thesauri, classification schemes, subject heading lists, 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. The Working Group also published a Working Draft of SKOS Simple Knowledge Organization System Primer.