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Understanding Call Numbers: What Call Numbers Mean

A guide to the Library of Congress call numbers used at Geisel Library.


The majority of books in Geisel Library are organized using the Library of Congress call number system.  This system arranges books on the shelf according to subject.

Because of this, once you find a book that's relevant to your topic, you can often find other relevant books to the left and right of it on the shelf.  This makes "browsing the shelf" an effective way to find multiple sources quickly.

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      Reading Call Numbers

      Every book, CD, and DVD in the library has a call number label on its spine.  This call number has four parts, not counting a code for the location of the item that may appear at the beginning (e.g., Ref for Reference).  Refer to the example at right to see an illustration of how this works.

      1) A one, two, or three letter code indicating the broad subject of the book.

      • Examples: BF (Psychology), D (World History), and DA (British History).
      • Our example: HM is the subject code for Sociology.

      2) A number that may have 1-4 digits, which is a code that corresponds to the narrower subject of the book.

      • Examples: 23, 805, 4340
      • Our example: HM206 relates to the sociology of human ecology.

      3) A letter followed by a number, which often relates to the last name of the book's author.  Note that some books will have more than one of these.

      • Examples: .M28 B5, .L54 C845, .P32
      • Our example: .D48 is a code for the author's last name, Diamond.

      4) A year, indicating the year that our copy of the book was published.  Other info in this part may include item or volume information.

      • Examples: 1967, 1995, 2008
      • Our example: 1997 is when our copy of "Guns, Germs, and Steel" was published.

      Example: Guns, Germs, and Steel

      Library of Congress classification

      To see a complete listing of the Library of Congress's call number categories, and the subjects they represent, see the Library of Congress Classification Outline.