The CIS Thesaurus contains the terms used to index documents in CISDOC, the bibliographic database of the International Labour Office's International Occupational Safety and Health Information Centre (CIS). To make it easy to find all the documents that refer to a particular subject, CIS always uses the same words, although the subject may be described in many different ways in different documents. In CISDOC, documents are always described in English and French, and an increasing number are being described in Spanish as well. These descriptions include the index entries, so the CIS Thesaurus is fully trilingual.