What is the Dewey Decimal System?

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  • Last Modified Date: 07 December 2018
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The Dewey Decimal Classification system, sometimes abbreviated DDC, is a method of categorizing books in a library by subject matter. It is a numerical system using groupings of ten — i.e. there are ten major classes, each of which has ten divisions, each of which has ten sections — and books are placed on the shelf in numerical order. The system was created by Melvil Dewey in 1876 and is currently owned by the Online Computer Library Center in Dublin, Ohio, which acquired the trademark in 1988.

The Dewey Decimal system is extensively used in United States libraries, and a system based on it, the Universal Decimal Classification, is used around the world. Before it was developed, there was no standard of organizing library books, and most systems in use were quite arbitrary and inefficient. Today, this system is used in about 95% of United States school and public libraries, while the Library of Congress Classification system, first developed in 1897, is more widely used in government and university libraries.

The call numbers in the Dewey Decimal system provide increasingly specific information about the book when read from left to right. There are three numerals in each, followed by a decimal point, which may be followed by more numerals to more specifically categorize the book. The second line of the call number consists of the first few letters of the author's name, which may be used to alphabetize books with the same numerical classification.


Though fictional works are classified within the 800 class, Literature, many libraries choose to have a separate section for fiction in which the books are alphabetized by author. Literary works in the Dewey Decimal System are subdivided by their original language and then by form — poetry, fiction, or essay, for example — so that all works of fictional prose are not in a single place. Making a separate section for fiction both caters to patrons who are only interested in novels and keeps the 800 section from becoming overgrown.

The ten main classes of the Dewey Decimal system are as follows:

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

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Post 9

@clintflint - When you consider that library science is actually a degree at university where you are basically taught Dewey decimal system classification (among other things, of course) it's not surprising that you had difficulty. Any system that can categorize every topic in human thought and experience is going to be very dense and difficult to interpret, although the Dewey system is as good as anything I can imagine.

I wonder how often (if ever) they get a new topic that needs to be decided on. Something that could go in more than one area, for example.

I wonder if there's a place where they decide these things, or if it's up to each individual library.

Post 8
If you're used to the Dewey system it can actually be quite difficult to adapt to another system. When I first got to university, they used a different system, I'm not sure which one, but it definitely wasn't the Dewey system.

And, I'm ashamed to say, instead of asking for help, I just kind of wandered around for the first year, hoping that I would find the right books (although I never did). The library was six or seven stories, all packed with books, so it's a wonder I got anything done at all.

The next year, I swallowed my pride and went to one of the open days so that I could learn how to find books and I did much better after that. Don't take it for granted that you'll be able to figure out a system.

Post 2

While many libraries do store books of poetry or plays in the 800s, fiction is usually found on the other side of the library, alphabetized by last name.

Mysteries and sci-fi have become such popular genres that they are kept separate even from the other fictional novels. Mysteries are alphabetized by themselves by the author's last name, as are sci-fi books.

Post 1

this could really help a lot, especially to us students. thank you so much!

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