Dewey Decimal Classification

The Dewey Decimal Classification (DDC), or Dewey Decimal System, is a proprietary library classification system first published in the United States by Melvil Dewey in 1876. It has been revised and expanded through 23 major editions, the latest issued in 2011, and has grown from a four-page pamphlet in 1876 with fewer than 1,000 classes to a four volume set. It is also available in an abridged version suitable for smaller libraries. It is currently maintained by the Online Computer Library Center (OCLC), a non-profit cooperative that serves libraries. OCLC licenses access to an online version for catalogers called WebDewey.

The Decimal Classification introduced the concepts of relative location and relative index which allow new books to be added to a library in their appropriate location based on subject. Libraries previously had given books permanent shelf locations that were related to the order of acquisition rather than topic. The classification's notation makes use of three-digit Arabic numerals for main classes, with fractional decimals allowing expansion for further detail. Using Arabic numerals for symbols, it is flexible to the degree that numbers can be expanded in linear fashion to cover special aspects of general subjects. A library assigns a classification number that unambiguously locates a particular volume in a position relative to other books in the library, on the basis of its subject. The number makes it possible to find any book and to return it to its proper place on the library shelves. The classification system is used in 200,000 libraries in at least 135 countries.

The major competing classification system to the Dewey Decimal system is the Library of Congress Classification system created by the U.S. Library of Congress.

Melvil Dewey (1851–1931) was an American librarian and self-declared reformer. He is best known for the Decimal System that he created, but he also was a founding member of the American Library Association and can be credited with the promotion of card systems in libraries and business. He developed the ideas for his library classification system in 1873 while working at Amherst College library. He applied the classification to the books in that library, until in 1876 he had a first version of the classification. In 1876, he published the classification in pamphlet form with the title A Classification and Subject Index for Cataloguing and Arranging the Books and Pamphlets of a Library. He used the pamphlet, published in more than one version during the year, to solicit comments from other librarians. It is not known who received copies or how many commented as only one copy with comments has survived, that of Ernest Cushing Richardson. His classification system was mentioned in an article in the first issue of the Library Journal and in an article by Dewey in the Department of Education publication "Public Libraries in America" in 1876. In March 1876, he applied for, and received copyright on the first edition of the index. The edition was 44 pages in length, with 2,000 index entries, and was printed in 200 copies.

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