SWIB14 presentation Over time, Knowledge Organization Systems such as thesauri and classifications undergo lots of changes, as the knowledge domains evolve. Most SKOS publishers therefore put a version tag on their vocabularies. With the vocabularies interwoven in the open web of data, however, different versions may be the base for references in other datasets. So, updates by "third parties" are required, in indexing data as well as in mappings from or to other vocabularies. Yet answers to simple user questions such as "What's new?" or "What has changed?" are not easily obtainable. Best practices and shared standards for communicating changes precisely and making them (machine-) actionable still have to emerge. STW Thesaurus for Economics currently is subject to a series of major revisions. In a case study we review the amount and the types of changes in this process, and demonstrate how versioning in general and difficult types of changes such as the abandonment of descriptors in particular are handled. Furthermore, a method to get a tight grip on the changes, based on SPARQL queries over named graphs, is presented. And finally, the skos-history activity is introduced, which aims at the development of an ontology/application profile and best practices to describe SKOS versions and changes.