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Dewey Decimal Classification System: A Dewey Primer

This LibGuide describes Dewey Decimal call numbers and how books are arranged on the shelves using this system.

Dewey Basics

Many public libraries and some other library systems use Dewey Decimal numbers to classify or arrange books and other items in their collections.  This call number is like an address which identifies the shelf location of the item.   The PCC Library traditionally has arranged its collections using the Dewey system, but is now transitioning to the Library of Congress System.   You will find the newer books, the textbook collection and the reference collection arranged by LC numbers and the older circulating books arranged by Dewey numbers.   To find the call number and library location use the WorldShare search box below. 

Dewey: Ten Main Classes

000 Computer science, information & general works
100 Philosophy & psychology
200 Religion
300 Social sciences
400 Language
500 Science
600 Technology
700 Arts & recreation
800 Literature
900 History & geography

These broad subject disciplines are further divided into the hundred divisions.  Numbers are placed after a decimal point to further identify material more specifically by subject.   Examples of dewey numbers:

900    represents History & geography

  • 940     represents general history of Europe.  
  • 940.1    represents Middle ages 476 - 1453.


300     represents the Social Sciences

  • 320 represents Political Science (politics and government)
  • 324   The Political Process
  • 324.2   Political parties
  • 324.273   Parties of the United States
  • 324.2736    Democratic party

You can see from the above examples that as the number is extended the area of study becomes more specific or has a narrower focus. 

The Author Number

The letter and number which follows the Dewey call number is used to place the books in author order .   Sometimes a book does not have a main author and the first word in the title is used instead.   If for example the library receives a book about the psychology of dreams and it is written by an author with the last name Robbins, its number would be 154.63 R 1

After that, if the library purchased another book about the psychology of dreams and the authors' name also began with "R" it would receive the number 154.63 R 2.   Sometimes multiple books by the same author and dealing with the same subject are purchased.   If a second book by Robbins about the psychology of dreams were to be purchased, its number would be 154.63 R 1-2.

Search books, articles and more: the PCC Library Catalog

A single search box covers our catalog of books and DVDs, as well as a large number of the periodical articles in our collection. You can search All, or you can use the tabs above the search box to narrow your search to Articles or Books.

Start your search here!

Web Sites about Dewey Call Numbers