Medical Subject Headings (MeSH) is a comprehensive controlled vocabulary for the purpose of indexing journal articles and books in the life sciences; it can also serve as a thesaurus that facilitates searching. Created and updated by the United States National Library of Medicine (NLM), it is used by the MEDLINE/PubMed article database and by NLM's catalog of book holdings. MeSH was introduced in 1963. The yearly printed version was discontinued in 2007 and MeSH is now available online only.[2] It can be browsed and downloaded free of charge through PubMed. Originally in English, MeSH has been translated into numerous other languages and allows retrieval of documents from different languages.

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The 2009 version of MeSH contains a total of 25,186 subject headings, also known as descriptors.[2] Most of these are accompanied by a short description or definition, links to related descriptors, and a list of synonyms or very similar terms (known as entry terms). Because of these synonym lists, MeSH can also be viewed as a thesaurus.[3]