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 various other catalogues and bibliographic databases of Estonia.

The database of EMS enables
- to browse subject terms by subject fields
- to browse form/genre and chronological terms
- 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, in the digital archive Digar, in the database of the Estonian national bibliography ERB, 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
- to download data as mnemonic Marc21, machine-readable Marc21 or MarcXML record.

EMS includes about 64 000 preferred and nonpreferred terms. 

The Estonian Subject Thesaurus is managed by the Estonian Libraries Network Consortium, areas of responsibility are divided between libraries.

Contact: ems@elnet.ee