The Semantic Web Deployment Working Group has published the Last Call Working Draft 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. The SKOS data model provides a standard, low-cost migration path for porting existing knowledge organization systems to the Semantic Web. SKOS also provides a light weight, intuitive language for developing and sharing new knowledge organization systems. It may be used on its own, or in combination with formal knowledge representation languages such as the Web Ontology language (OWL). Comments are welcome through 03 October. The group has also published an update of the companion SKOS Primer.