The CIS Thesaurus is the trilingual (English, French, Spanish) source of terms used to index the CIS bulletin and database. It can also supply "meta" tags for indexing Web pages, and its system of facet codes has been used to organize occupational safety and health libraries.

The terms are organised hierarchically according to their specificity. Each term is associated with a facet code, which is a combination of letters or numbers that indicates the place of the term in the hierarchy. The CIS Thesaurus represents a slight variation from the "classic" thesaurus paradigm: because terms and their facets are not generally added to the thesaurus unless they have been used to index a document, it may happen that there is no generic term covering one or more terms at a particular level in the thesaurus, although there may be an even broader term further up the hierarchy.

The Thesaurus is maintained as a database at CIS. At intervals, the data are published in two formats: on paper and on CD-ROM. The printed version (1999) presents the terms in three orders, thematically by facet code, alphabetically and, in the case of chemical substances, numerically by Chemical Abstracts Service Registry Number. The CD-ROM edition (2001) provides easy navigation within the hierarchical structure and is searchable in English, French or Spanish.