What's the DDC?

The Dewey Decimal Classification (DDC) system is a general knowledge organization tool that is continuously revised to keep pace with knowledge. The system was conceived by Melvil Dewey in 1873 and first published in 1876. The DDC is published by OCLC Online Computer Library Center, Inc. OCLC owns all copyright rights in the Dewey Decimal Classification, and licenses the system for a variety of uses.


Who's responsible for the DDC?

One of Dewey's great strengths is that the system is developed and maintained in a national bibliographic agency, the Library of Congress. The Dewey editorial office is located in the Dewey Section of the Library of Congress, whose classification specialists and Cataloging-in-Publication partner libraries annually assign over 90,000 DDC numbers to records for works cataloged by the Library. Having the editorial office within the Dewey Section enables the editors to detect trends in the literature that must be incorporated into the Classification. The editors prepare proposed schedule revisions and expansions, and forward the proposals to the Decimal Classification Editorial Policy Committee (EPC) for review and recommended action. EPC is a ten-member international board whose main function is to advise the editors and OCLC on matters relating to changes, innovations, and the general development of the Classification. EPC represents the interests of DDC users; its members come from national, public, special, and academic libraries, and from library schools.


Who uses the DDC?

The DDC is the most widely used classification system in the world. Libraries in 138 countries use the DDC to organize and provide access to their collections, and DDC numbers are featured in the national bibliographies of 62 countries. Libraries of every type apply Dewey numbers on a daily basis and share these numbers through a variety of means (including WorldCat, the OCLC Online Union Catalog). Dewey is also used for other purposes, e.g., as a browsing mechanism for resources on the web. The DDC has been translated into over thirty languages. Translations of the latest full and abridged editions of the DDC are completed, planned, or underway in Arabic, French, German, Icelandic, Indonesian, Italian, Norwegian, Portuguese, Swedish, Turkish, and Vietnamese.


In what formats is the DDC published?

The DDC is published in full and abridged editions and appears in print and electronic versions. The latest full edition is the 23rd (DDC 23), published in 2011, and the latest abridged edition is the 15th (Abridged 15), published in 2012. The abridged edition is a logical truncation of the notational and structural hierarchy of the corresponding full edition on which it is based, and is intended for general collections of 20,000 titles or less. WebDewey, the electronic version of the DDC is updated frequently and contains additional index entries and mapped vocabulary. The electronic versions and supplemental web postings are the chief sources of ongoing updates to the DDC. New numbers and changes to the DDC are posted regularly.


How is the DDC structured?

The DDC is built on sound principles that make it ideal as a general knowledge organization tool: meaningful notation in universally recognized Arabic numerals, well-defined categories, well-developed hierarchies, and a rich network of relationships among topics. In the DDC, basic classes are organized by disciplines or fields of study. At the broadest level, the DDC is divided into ten main classes, which together cover the entire world of knowledge. Each main class is further divided into ten divisions, and each division into ten sections (not all the numbers for the divisions and sections have been used). The main structure of the DDC can be seen at Clicking a main class there will lead to the divisions below it; clicking a division there will lead to the sections below it; etc.

The first digit in each three-digit number represents the main class. For example, 600 represents technology.

The second digit in each three-digit number indicates the division. For example, 600 is used for general works on technology, 610 for medicine and health, 620 for engineering, 630 for agriculture.

The third digit in each three digit number indicates the section. Thus, 610 is used for general works on medicine and health, 611 for human anatomy, 612 for human physiology, 613 for personal health and safety.

Arabic numerals are used to represent each class in the DDC. A decimal point follows the third digit in a class number, after which division by ten continues to the specific degree of classification needed.

A subject may appear in more than one discipline. For example, "clothing" has aspects that fall under several disciplines. The psychological influence of clothing belongs in 155.95 as part of the discipline of psychology; customs associated with clothing belong in 391 as part of the discipline of customs; and clothing in the sense of fashion design belongs in 746.92 as part of the discipline of the arts.


How do I find out more about the DDC?

The Dewey web site contains up-to-date information about the DDC, DDC products and services, and DDC licensing. For more information about the structure and application of the Dewey Decimal Classification, consult the Introduction to the Dewey Decimal Classification (also available from WebDewey and in volume 1 of DDC 23). A more in-depth introduction to the Dewey Decimal Classification may be found in Dewey Decimal Classification: Principles and Application, 3d ed., by Lois Mai Chan and Joan S. Mitchell (Dublin, Ohio: OCLC, 2003). Training materials for the DDC, including modules on general principles governing the operation of the DDC, as well as modules on the structure and use of specific tables and main classes are available at no charge.


How do I get hold of the DDC?

The print versions of DDC 23 (4 vols.) and Abridged 15 are available for purchase directly from OCLC and its authorized distributors. Access to the electronic version -- WebDewey -- is offered by OCLC and its authorized distributors upon payment of an annual subscription fee. Full ordering instructions for print and electronic versions are given here.


What legal stuff should I bear in mind?

All copyright rights in the Dewey Decimal Classification are owned by OCLC. Connexion, DDC, Dewey, Dewey Decimal Classification, OCLC, WebDewey, and WorldCat are registered trademarks of OCLC. All other service names are registered with their respective companies. OCLC considers requests for licensing the DDC database. To request a licensing proposal, please send an e-mail message here, describing in detail your proposed use of the DDC.

Last update: August 6, 2013