A digital library is, like a traditional library, a collection of books and reference materials. Unlike a traditional library, however, the collection of a digital library is, as you would expect, digital, and is usually served over the World Wide Web. Some of the largest and most successful digital libraries are Project Gutenberg, ibiblio and the Internet Archive.

Some people have criticized that digital libraries are hampered by copyright law, because works cannot be shared over different periods of time in the manner of a traditional library. The content is, in many cases, public domain or self-generated content only. Some digital libraries, such as Project Gutenberg, work to digitize out-of-copyright works and make them freely available to the public.

Genre publisher Baen Books has made many of its titles available electronically through the Baen Free Library.

See List of digital library projects for an extensive listing.

Alternate definition:

The Digital Library is:

  • The collection of services
  • And the collection of information objects
  • That support users in dealing with information objects
  • And the organization and presentation of those objects
  • Available directly or indirectly
  • Via electronic/digital means.

-- The Scope of the Digital Library, draft Prepared by Barry M. Leiner for the DLib Working Group on Digital Library Metrics, January 16, 1998

While the first definition is focussed on ebooks, this is much more general. Information objects can be anything expressed in a digital format: books, journal articles, maps, picture, sounds, etc. The important thing is that, like a "regular" library, the Digital Library is organised to store and make accessible the objects it contains, but the storage and retrieval methodologies used differ in being "electronic".