Dewey Decimal Classification

The classification began as Melvil Dewey’s attempt to create a compact, expandable arrangement for Amherst College Library. Its first edition appeared in 1876, when the system used decimal notation to divide subjects into increasingly specific categories.¹ The ten main classes begin with 000 for general works and computer science, followed by 100 philosophy and psychology, 200 religion, 300 social sciences, 400 language, 500 science, 600 technology, 700 arts and recreation, 800 literature, and 900 history and geography.²

Each class is divided into ten divisions and each division into ten sections, producing a numerical hierarchy rather than a simple alphabetical list. The hierarchy is conceptual: neighboring numbers usually indicate related subjects, although editorial decisions and historical compromises can make the sequence uneven.

Decimal notation lets DDC express both broad subjects and narrow topics in a short, sortable form. A number such as 500 identifies science broadly, while added digits refine the subject; a decimal point improves readability but does not change the underlying numerical order.¹ Tables and instructions allow classifiers to add geographic, chronological, literary, and form details when the schedules authorize them.

Libraries commonly place a DDC number on a book’s spine as part of a call number, often combining it with an author or title mark. The result groups works by subject while distinguishing individual items. Classification is separate from cataloging: a catalog record describes and provides access to an item, whereas DDC primarily supplies a systematic subject location. DDC can therefore support browsing even when readers do not know a book’s title.

DDC has been revised through successive editions, so its schedules are editorial documents rather than a permanently fixed map of knowledge. The system is now maintained and licensed by OCLC, whose editorial process incorporates specialist advice, proposed changes, and continuing adjustments for new subjects and terminology.¹

Translations and national adaptations have extended DDC well beyond its American origin; it is used in many public, school, academic, and national libraries around the world.¹ Its international reach reflects the usefulness of a shared notation, but adaptations may reflect local languages, literature, religions, and administrative needs. DDC is distinct from the Library of Congress Classification, which uses an alphanumeric structure and is especially prominent in large research libraries in the United States.⁴ It also differs from the Universal Decimal Classification, an internationally developed system derived from DDC but expanded with additional symbols and relationships.

DDC’s decimal principle is more flexible than its familiar ten-class summary suggests. It can express interdisciplinary subjects, geographic areas, literary forms, and historical periods through combinations authorized in its schedules, while relative indexes help classifiers move from ordinary language to the appropriate number.¹

The system also reveals the cultural assumptions of the period in which it was developed. The placement of religion, literature, social groups, and regions has been revised over time, yet classification inevitably involves judgments about which subjects are central, adjacent, or subdivided. Libraries may therefore modify, abridge, or supplement DDC rather than apply every schedule mechanically. Digital catalogs have reduced the system’s role as the sole discovery tool, but its stable notation remains useful for shelf browsing, collection management, statistical reporting, and multilingual cooperation. The system’s continuing revisions show that a classification can be both an organizational technology and an evolving intellectual framework.

Main class

One of DDC’s ten broad knowledge categories, numbered from 000 through 900.

Notation

The symbols used to represent subjects; DDC primarily uses Arabic numerals and decimal subdivisions.

Schedule

The structured list of classes, subdivisions, notes, and instructions used to assign DDC numbers.

Call number

A label that identifies an item’s subject location and distinguishes it from other items in a library collection.

Relative index

An alphabetical index that connects terms and concepts to their possible DDC locations.