Library of Congress Subject Headings

The Library of Congress Subject Headings (LCSH) comprise a thesaurus (in the information science sense, a controlled vocabulary) of subject headings, maintained by the United States Library of Congress, for use in bibliographic records. LC Subject Headings are an integral part of bibliographic control, which is the function by which libraries collect, organize and disseminate documents. LCSHs are applied to every item within a library’s collection, and facilitate a user’s access to items in the catalogue that pertain to similar subject matter. If users could only locate items by ‘title’ or other descriptive fields, such as ‘author’ or ‘publisher’, they would have to expend an enormous amount of time searching for items of related subject matter, and undoubtedly miss locating many items because of the ineffective and inefficient search capability.

Subject heading classification is a human and intellectual endeavor, where trained professionals apply topic descriptions to items in their collections. Naturally, every library may choose to categorize the subject matter of their items differently, without a uniform consentaneous standard. The widespread use and acceptance of the Library of Congress Subject Headings facilitates the uniform access and retrieval of items in any library in the world using the same search strategy and LCSH thesaurus, if the correct headings have been applied to the item by the library. Thus, LCSH decisions involve a great amount of debate and even controversy in the library community.

Despite LCSH's wide-ranging and comprehensive scope, there are libraries where the use of LCSH is not ideal or effective. To deal with these types of collections and user communities, other subject headings may be required. The United States National Library of Medicine developed Medical Subject Headings (MeSH) to use on its many health science databases and collection. Many university libraries may not apply both LCSH and MeSH headings to items. In Canada, the National Library of Canada worked with LCSH representatives to create a complementary set of Canadian Subject Headings (CSH) to access and express the topic content of documents on Canada and Canadian topics.

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