A library is a collection of information, sources, resources, books, and services, and the structure in which it is housed: it is organized for use and maintained by a public body, an institution, or a private individual. In the more traditional sense, a library is a collection of books. The term can mean the collection, the building that houses such a collection, or both.

Public and institutional collections and services may be intended for use by people who choose not to — or cannot afford to — purchase an extensive collection themselves, who need material no individual can reasonably be expected to have, or who require professional assistance with their research.