Where Google took over with “indexing”.
The Dewey Decimal Classification (DDC), commonly known as the Dewey Decimal System, is a proprietary method of organizing library collections based on subject matter. Introduced by Melvil Dewey in 1876, the system was initially outlined in a 44-page pamphlet but has since evolved into multiple volumes, undergoing 23 major revisions—the latest published in 2011. An abridged version is also available for smaller libraries. Today, the system is maintained by OCLC, a nonprofit cooperative serving libraries, which provides online access to WebDewey, a continuously updated resource for catalogers.
The DDC revolutionized book organization by introducing relative location and index concepts. Previously, books were shelved permanently based on acquisition order rather than topic. The Dewey system uses three-digit numbers to classify main subjects, with fractional decimals offering further precision. Libraries assign classification numbers to books, ensuring they are grouped by subject and easily located. This numerical system enables efficient retrieval and placement of books on shelves.
Widely adopted, the Dewey Decimal System is used in over 200,000 libraries across 135 countries, making it one of the most influential classification systems in the world.