The Zthes family of specifications facilitate interoperability for applications that deal with thesauri – semantic hierarchies of terms as described in ISO 2788 and ANSI/NISO Z39.19.
* The core specification in the Zthes suite is an abstract model for thesaurus terms.
* This model is made concrete by an XML format for representing thesauri according to this model.
* Additional specifications show how queries into Zthes-compliant thesauri may be expressed using CQL, and how such thesauri may be accessed using the REST-like SRU protocol and the SOAP-based SRW web-service, or using the ANSI/NISO Z39.50 information retrieval protocol,
Because the Zthes specification work was done largely in the UK, « Zthes'' is pronounced « Zed-thezz''. However, « Zee-thezz'' is an acceptable variant.