A private library is an institutional, corporate, or otherwise non-public collection of written materials. It may be open to the public according to the terms of its use, but is not owned by the public or the state.

Public access and public ownership are different characteristics. A private library may admit outside readers on its own terms, while a public library is maintained by government for the benefit of the public. Admission rules alone do not establish ownership.

An educational library belongs to a school or university, including a privately owned institution. An archive is organized primarily for preservation and reference, which is a different purpose from maintaining a collection for library use.