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Library Classification Systems
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Library Classification Systems: organization by subject

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Within a collection, materials are typically organized by subject. Librarians assign a call number based on a work's subject. The sources are then shelved by call number so that anyone browsing the shelves will find most of the titles on a subject together.

There are 2 main subject classification systems that translate a work's subject and author or title into a code (call number) that determines where it will be shelved.

The examples below illustrate how call numbers are assigned for the book, Battle in Seattle by Janet Thomas, printed in 2000, about the demonstrations during the WTO summit in Seattle.


Library of Congress: Used in most college, university, and research libraries because it handles large collections.


Dewey Decimal: Used in most public and school libraries because it is more effective for smaller collections.

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For more information about these classification systems, follow the links below.

Library of Congress

Dewey Decimal

Superintendent of Documents (SuDocs) (for US government documents)





Battle in Seattle by Janet Thomas

© University of Washington Information Literacy Learning 2001