A library is a collection of sources, resources, 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.