The Estonian Subject Thesaurus is a universal controlled vocabulary in Estonian for indexing and searching various library material.

The official name of the thesaurus is "Eesti märksõnastik" and its official abbreviation is EMS. In English the thesaurus is called "Estonian Subject Thesaurus".

The subject terms from EMS are used

• in the online catalogue ESTER
• in the database of Estonian articles ISE
• in the union catalogue URRAM of the Estonian public libraries
• in the other catalogues and bibliographic databases of Estonia.

The database of EMS enables

• to browse subject terms by subject fields
• to search terms by exact match or by part of word
• to search terms by English equivalent
• to view search results as word lists or as full records
• to search by every term in the online catalogue ESTER, in the database of Estonian articles ISE or in Google
• to print, e-mail or save into file selected word lists or full records
• to subscribe current awareness service for new, changed and deleted subject terms.