System of arrangement adopted by a library to enable patrons to locate its materials quickly and easily.
Classifications may be natural (e.g., by subject), artificial (e.g., by alphabet, form, or numerical order), or accidental (e.g., chronological or geographic). They also vary in degree; some have minute subdivisions while others are broader. Widely used systems include the Dewey Decimal Classification , the Library of Congress Classification, the Bliss Classification, and the Colon Classification; special libraries may devise their own unique systems.