Essentially the same as the CD-ROM in appearance, capability, and storage capacity, the Web CD-ROM expands upon the functionality of the CD-ROM-based e-book and eliminates many of the potential drawbacks of this form of electronic publication. The Web-CD is a CD-ROM that uses the capabilities of hypertext and hot links found in almost all e-books on CD-ROM and includes hot keys to web-based URLs. By this simple act of linking to web sites, the Web-CD thus makes it possible for the author to construct the narrative on a single CD-ROM, include a wide variety of visual and sound elements on that disk, but then also, through links to the URLs of digital archives of texts and images, online bibliographies, related web sites with parallel narratives and interpretations, and aggregates of all these, to vastly expand the scope and documentation of his or her work.

For example, many of the hot keys employed in a document are hyperlinked to sites within the document itself. However, clicking on hotkeyed text for a web site will activate the reader's web browser, dial up its server, connect with the URL indicated by the link, and bring the reader to the page on the World Wide Web. Such simple functionality is the essence of the Web-CD; and by the judicious use of such links author and the publisher can realize an immense broadening of their documentation, the scope of their subject and its interpretation.

Web-CDs have long been a favorite of commercial reference publishers, since they can offer sufficient information on a single CD or series of disks to provide the reader with an adequate treatment of the subject; but then, usually through links to proprietary web sites, can then expand the reader's options and information base. The Complete National Geographic is a fine example of this capability that allows the reader to log on to the National Geographic web site from the CD-ROM, access back issues in full text, and activate other capabilities. While commercial Web-CDs often involve fees for such access, their value to the historian is obvious: links can be made to a wide variety of public-domain or no-fee sites that add great value to the original CD-ROM and encourage the purchaser - private or institutional - to invest in the individual disk. Thus the Web-CD can be considered a gateway and an introduction to a much broader field of resources.

One of the chief disadvantages of the Web-CD is precisely its great strength: with the rapidly changing composition of the World Wide Web, links to URLs are constantly appearing and disappearing; and URLs themselves are often being shut down or not maintained regularly. Thus a disk full of web links on CD-ROM might, in a very few years at best, become obsolete, and at worst misleading and frustrating to the researcher and student. With regular updates and reissues of the original CD-ROM however, such problems can be eliminated, and the Web-CD, like the CD-ROM, can be maintained and enriched by the same process as regular revisions to a print textbook. Factors of the author's and publisher's time and expense come into play here to the same - or perhaps greater - degree as in traditional print revision. Authors and publishers therefore need to carefully weigh the advantages, disadvantages, and sustainability of such formats before beginning an electronic title.