Dewey Decimal Classification: What It Is and How to Use It

The Dewey Decimal Classification, often abbreviated as DDC, is a knowledge organisation system used to group books according to their subject. The system was devised by Melvil Dewey and first published in 1876; today it is published and updated by OCLC.

Each subject is assigned a numerical code. The initial digits identify a broad subject, while the following digits make it possible to describe increasingly specific topics. In this way, books covering similar subjects can be shelved and searched according to a consistent criterion.

The DDC does not replace the title, author, ISBN or subject headings: it is an additional piece of information in the bibliographic record and helps organise the collection both physically and logically.

🔗 Official OCLC information about the Dewey Decimal Classification

First digit
Indicates one of the ten main classes.

First two digits
Identify a more specific division.

First three digits
Identify a section of the subject.

Decimal digits
Allow the subject to be described in greater detail.

000 – Computer science, information and general works

100 – Philosophy and psychology

200 – Religion

300 – Social sciences

400 – Language

500 – Science and mathematics

600 – Technology and applied sciences

700 – Arts and recreation

800 – Literature

900 – History and geography

Before assigning a code, the main subject of the book must be identified. The title may provide an indication, but it is often necessary to consult the table of contents, introduction, publisher description or other bibliographic data.

A small library can use relatively broad codes. A large or specialised catalogue may require more precise classification, with additional decimal digits.

Similar books should be classified using consistent criteria. It is useful to document any internal rules, especially when several operators work on the same catalogue.

PowerBK allows the Dewey code to be recorded within the book record and used together with the other bibliographic data. The code can then be searched, edited, printed and exported using the functions available in the software.

Integrating the DDC with title, author, ISBN, shelving location, category, barcode and loan information makes it possible to create a structured archive, useful both for small personal collections and for school, association or professional libraries.

It is important to distinguish the Dewey code from the physical location. The former describes the subject of the book; the latter indicates where the volume is physically located, for example a room, bookcase, shelf or section.

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The Dewey Decimal Classification is a system published and managed by OCLC. For professional classification activities, users should refer to the available official editions and tools.

This page provides an introductory explanation and does not replace the official Dewey documentation.

Question: Is Dewey classification only useful for large libraries?
Answer: No. It can also be useful for school libraries, associations and private collections, by choosing a level of detail proportionate to the size of the catalogue.

Question: Is the Dewey code the same as the ISBN?
Answer: No. The ISBN identifies a specific publication, edition and format; the Dewey code instead describes the subject of the work.

Question: Can two books have the same Dewey code?
Answer: Yes. Books covering the same subject may share the same code and are then distinguished by author, title, ISBN, inventory number or shelving location.