About the Dewey Decimal System

First developed by Melvil Dewey in 1876, and modified greatly over the years, the Dewey Decimal Classification (DDC) System has become the most commonly used classification system in American libraries.

The Dewey Decimal Classification (DDC) System organizes all information into ten main classes. These ten classes are then subdivided further into 100 divisions and 1000 sections. Through this hierarchical system, information is first categorized with other generally similar information, then more similar materials, and finally only those items nearly identical in topic.

Works are classified by subject, with a system of extensions also enabling specific subject relationships, geographical area, and time periods to be encoded into the classification numbers. Books are kept on the shelf in increasing numerical order.

Using the Dewey Decimal System

All books have at least a 100's level classification number but are otherwise at variable lengths. While the 100 division (the first three digits of the classification number) is read as a whole number, all numbers after the decimal point are taken one digit at a time. (With "0" being the smallest possible number, "9" the highest). Therefore, 300.456 would be shelved before 300.72, because 4 is lower than 7.

If you haven't had much experience using the Dewey Decimal System, it can be difficult to remember to take the numbers following the decimal point one at a time. Try to remember that each digit represents some topical grain of similarity. As the digits get stacked on, one by one, new subject depths are being encoded.