A digital library is a library in which collections are stored in digital formats (as opposed to print, microform, or other media) and accessible by computers. The digital content may be stored locally, or accessed remotely via computer networks. A digital library is a type ofinformation retrieval system.
In the context of the DELOS, a Network of Excellence on Digital Libraries, and DL.org, a Coordination Action on Digital Library Interoperability, Best Practices and Modelling Foundations, Digital Library researchers and practitioners produced a Digital Library Reference Model which defines a digital library as: "A potentially virtual organisation, that comprehensively collects, manages and preserves for the long depth of time rich digital content, and offers to its targeted user communities specialised functionality on that content, of defined quality and according to comprehensive codified policies."
Actually, this document contains a Digital Library Manifesto which introduces the three types of relevant ‘systems’, i.e. Digital Library, Digital Library System, and Digital Library Management System. It describes the main concepts characterising these systems, i.e., organisation, content, user, functionality, quality, policy and architecture. It introduces the main roles that actors may play within digital libraries, i.e., end-user, manager and software developer. Finally, it describes the reference frameworks needed to clarify the DL universe at different levels of abstraction, i.e., the Digital Library Reference Model and the Digital Library Reference Architecture.
The first use of the term digital library in print may have been in a 1988 report to the Corporation for National Research Initatives. The termdigital libraries was first popularized by the NSF/DARPA/NASA Digital Libraries Initiative in 1994. These draw heavily on As We May Think by Vannevar Bush in 1945, which set out a vision not in terms of technology, but user experience. The term virtual library was initially used interchangeably with digital library, but is now primarily used for libraries that are virtual in other senses (such as libraries which aggregate distributed content).
A distinction is often made between content that was created in a digital format, known as born digital, and information that has been converted from a physical medium, e.g., paper, by digitizing. The term hybrid library is sometimes used for libraries that have both physical collections and digital collections. For example, American Memory is a digital library within the Library of Congress. Some important digital libraries also serve as long term archives, for example, the Eprint arXiv, and the Internet Archive.