The Value Set Authority Center (VSAC) is a value set authoring and repository for value sets. It is the source of truth for value sets for CMS's electronic clinical quality measures. The National Library of Medicine maintains the VSAC and provides downloadable access to the value sets and the Binding Parameter Specification. The VSAC provides users with tools to search existing value sets, create new value sets, and maintain value set content consistent with current versions of the terminologies they use. Use requires a free UMLS license.