Dewey Decimal Classification

Dewey Decimal Classification summaries

A Brief Introduction to the Dewey Decimal Classification

Links to contents
[History and Current Use] [Development] [Editions] [Structure and Notation] [Hierarchy] [Arrangement – Volume 1Volume 2Volume 3Volume 4]
[Entries] [Number Building] [More Information]
[First Summary – The Ten Main Classes] [Second Summary – The Hundreds Divisions] [Third Summary – The Thousands Sections]
[100] [200] [300] [400] [500] [600] [700] [800] [900]

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History and Current Use

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.

The DDC is the most widely used classification system in the world. Libraries in more than 135 countries use the DDC to organize and provide access to their collections, and DDC numbers are featured in the national bibliographies of more than 60 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, Chinese, French, German, Greek, Hebrew, Icelandic, Italian, Korean, Norwegian, Russian, Spanish, and Vietnamese.


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 Decimal Classification Division of the Library of Congress, where classification specialists annually assign over 110,000 DDC numbers to records for works cataloged by the Library. Having the editorial office within the Decimal Classification Division 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.


The DDC is published in full and abridged editions in print and electronic versions. 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 and Abridged WebDewey, the electronic versions of the full and abridged editions, respectively, are updated frequently and contain additional index entries and mapped vocabulary. The electronic versions and supplemental web postings are the chief sources of ongoing updates to the DDC. On the Dewey web site (, selected new numbers and changes to the DDC are posted monthly, and mappings between selected new Library of Congress Subject Headings (LCSH) and Dewey numbers are posted biweekly.

Structure and Notation

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 is presented in the DDC Summaries following this introduction. The headings associated with the numbers in the summaries have been edited for browsing purposes, and do not necessarily match the complete headings found in the schedules.

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

The second summary contains the hundred divisions. 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 summary contains the thousand sections. 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.


Hierarchy in the DDC is expressed through structure and notation. Structural hierarchy means that all topics (aside from the ten main classes) are part of all the broader topics above them. Any note regarding the nature of a class holds true for all the subordinate classes, including logically subordinate topics classed at coordinate numbers.

Notational hierarchy is expressed by length of notation. Numbers at any given level are usually subordinate to a class whose notation is one digit shorter; coordinate with a class whose notation has the same number of significant digits; and superordinate to a class with numbers one or more digits longer. The underlined digits in the following example demonstrate this notational hierarchy:

600 Technology
630 Agriculture and related technologies
636 Animal husbandry
636.7 Dogs
636.8 Cats

“Dogs” and “Cats” are more specific than (i.e., are subordinate to) “Animal husbandry”; they are equally specific as (i.e., are coordinate with) each other; and “Animal husbandry” is less specific than (i.e., is superordinate to) “Dogs” and “Cats.” Sometimes, other devices must be used to express the hierarchy when it is not possible or desirable to do so through the notation. Special headings, notes, and entries indicate relationships among topics that violate notational hierarchy.

Arrangement of the DDC

The print version of the latest full edition of the DDC, Edition 22, is composed of the following major parts in four volumes:

Volume 1

(A) New Features in Edition 22: A brief explanation of the special features and changes in DDC 22
(B) Introduction: A description of the DDC and how to use it
(C) Glossary: Short definitions of terms used in the DDC
(D) Index to the Introduction and Glossary
(E) Manual: A guide to the use of the DDC that is made up primarily of extended
discussions of problem areas in the application of the DDC. Information in the
Manual is arranged by the numbers in the tables and schedules
(F) Tables: Six numbered tables of notation that can be added to class numbers to
provide greater specificity
(G) Lists that compare Editions 21 and 22: Relocations and Discontinuations;
Reused Numbers

Volume 2

(H) DDC Summaries: The top three levels of the DDC
( I) Schedules: The organization of knowledge from 000–599

Volume 3

(J) Schedules: The organization of knowledge from 600–999

Volume 4

(K) Relative Index: An alphabetical list of subjects with the disciplines in which they are treated subarranged alphabetically under each entry