Today is the birthday of Melvil Dewey, the American librarian and educator, and inventor of the Dewey Decimal System of library classification. In memory of Melvil Dewey, today is the Dewey Decimal System Day.

The Dewey Decimal System, or Dewey Decimal Classification (DDC) is a numerical system of library classification first proposed by Dewey in 1876. Since its inception, the classification has been revised and expanded through 23 editions, the latest issued in 2011. Basically the system provides a framework within which a library book is assigned a ‘DDC number’ that unambiguously locates it in a specific space of shelving in the library, making it easy to find and return to its proper place.

For every subject, there's a Dewey classification number - in this case, environmental pollution.(© All Rights Reserved)
For every subject, there’s a Dewey classification number – in this case, environmental pollution.
(© All Rights Reserved)

The Dewey system classifies all books into 10 basic categories:

  • 000 – Computer science, Library and Information science & general work
  • 100 – Philosophy and psychology
  • 200 – Religion
  • 300 – Social sciences
  • 400 – Language
  • 500 – Science
  • 600 – Technology
  • 700 – Arts
  • 800 – Literature
  • 900 – History, geography & biography

While fiction books can also fit into the Dewey system (in the 800s), most libraries reserve the system for non-fiction works, rather classifying fiction using a basic alphabetic author-based system.

The Dewey system is used by no less than 200 000 libraries in more than 135 countries. It’s main competitor is the American Library of Congress Classification, which is more complex, but does have the advantage that it allows for the addition of new categories, which makes it more future-proof. The Library of Congress Classification is, however, very US-centric, and despite its increased adaptability it has been much less widely adopted than the Dewey system.

To what extent Dewey’s Decimal System will be able to continue remaining relevant as the knowledge landscape changes remains to be seen, but there can be no doubt that Melvil Dewey made a huge contribution to the classification and accessibility of knowledge the world over. And that must be a good thing.



  1. The source of endless frustration before it was available on the computer. I remember wading through stacks and stacks of card catalogs researching the esoteric.. These youngsters have it easy.

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