[[Image:HK Wan Chai Library Inside Bookcase a.jpg|thumb|A library book shelf in Hong Kong arranged using the Dewey classification]]
A '''library classification''' is a system structure of organization of knowledge by which sources are arranged and ordered very systematically. Library classifications are a notational system that represents the order of topics in the classification and allows items to be stored in that order. Library classification systems group related materials together, typically arranged as a hierarchical tree structure. A different kind of classification system, called a [[faceted classification]]<ref>{{Cite book|last=Publius|first=Vergilius Maro|url=http://worldcat.org/oclc/475463360|title=P. Virgilii Maronis Opera|date=1900|oclc=475463360}}</ref> system, is also widely used, which allows the assignment of multiple classifications to an object, enabling the classifications to be ordered in many ways.
