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Introduction to the Dewey Decimal system

The Dewey Decimal system is a classification system used by libraries to arrange books via subject. Each book is issued a shelfmark number, usually found on the spine of the book, and arranged in numerical order.

The first three digits refer to broad subject area, and are shelved in numerical order e.g. 945 is shelved before 946.

Dewey Decimal themed mug on a library bookshelf

000 Computer science, information and general work
100 Philosophy and psychology
200 Religion
300 Social sciences
400 Language
500 Science
600 Technology
700 Art and recreation
800 Literature
900 History and geography

After the three digits there is a decimal point and numbers after the decimal point show the sub-section of the subject area. Again they are shelved in numerical order e.g. 945.805 is shelved before 945.81.

After the numbers there are three letters which refer to the author or editor of the book and are in alphabetical order e.g. 945.805 TAB is shelved before 945.805 TRB.

Note: Journals (also called periodicals) always start PER, followed by three numbers and then the first three letters of the journal series e.g. PER720 ARC. Medical journals follow the same ordering, but start MED PER.

Play the gameA line of books showing Dewey Decimals

Sort the books into the correct order against the clock!

Watch the video

A short video overview of the Dewey Decimal system.


Duration: 1 minute 12 seconds