At some future time, this page should become a wiki. Until then, please feel free to add your opinion as to what is or is not Web Art by submitting a comment at the bottom of this page.
Art is always being redefined. Soon after art is well-defined an artist comes along with a work that is outside that definition. Everyone agrees that this work is truly a work of art. Thus the definition must be modified yet again.
It's likely that any definition with Web Art will eventually have to be so flexible as to be nearly meaningless.
But, for the moment, however, we are still at the beginning of time for Web Art. So, perhaps, we can set down some rules, establish a base-line for what is or is not Web Art. See, for example, the three unities of time, place and action relating to classical drama. And in doing so we throw down the gauntlet. We challenge artists to concur with or to challenge our definitions.
Space: Web Art is on the Internet. Anyone can access the work from any browser that is connected to the Internet.
Motion: Web Art is interactive. By clicking, typing, mousing or whatever the viewer has some or full control over the experience with the work.
Time: Web Art is instantly, theoretically eternal. 
The Highly Likely
The name of the work is a registered domain name. A typical name might be untitled59.com. This makes it easier to buy and sell the work because ownership of a domain name is easily transferable and legally binding.
The work is interesting to look at when there is no one interacting with the site as well as while the viewer is interacting with the site.
There are several pages on the site.
No links out. The work is self-contained. It stands by itself. If there must be links, the work must still be able to be considered a work of art even if the link to the outside fails.
There is data on the site or somewhere on the Internet regarding the intent of the site or the artist's statement or some other background on the purpose of the site.
There is a guest book to sign or some place on the Internet known as the correct place to leave a comment about the work. This place is easily located using Google. It should be intended that the comments shall last as long as the work itself. Although there may be some discussion between viewer and artist, the intention is to facilitate viewer-viewer discussion.
Once the work is signed and dated, the work is finished. There will always be artists who cannot finish a work. There will always be the temptation to FTP up a new file. But the thing that was there before cannot be un-seen.
Even when the artist retains copyright ownership of a web site, the ownership of the site and its contents are as transferable as any other artistic property. Just as paintings can be bought and sold, so can Web Art. Ownership of the web site could take many forms including:
- The domain name of the site
- A signed CD with the agreed contents
- A receipt noting the MD5 checksum for the entire contents of the site.
The Highly Desirable
Web Art does not sell, preach, recruit or teach. A mail order catalog may be stunningly beautiful but we would be reticent to put such a catalog an an art museum as a work of art. The more likely scenario is that the work is intended to be a work of art from the beginning. The purpose of Web Art is to inspire, to cause wonder, to be fun.
The artist-creator obtains on-going reward with increase in value. Perhaps each time a work of Web Art is sold a percentage of the sale price is offered to the artist.
It is very likely that the web site is built with Free Open Source Software (FOSS).
The web site is free of Digital Rights Management (DRM) and any other limitations that could diminish its life-expectancy.
The Being Cogitated
In the traditional arts there is a differentiation between high art such as painting, music, and literature with craft arts such as glassblowing, furniture making or jewelry-making. In a similar manner, web pages that can be used to create music (see Web Art Instrument) or to create graphic images should probably be thought of slightly differently that web sites are are purely artistic.On the other hand, because Web Art is interactive, creating new graphics or sounds is very likely to be an essential part of even the most artistic site. So it may be hard to tell where craft ends and art begins. Nothing new here.
 Because of the Wayback Machine, the Library of Congress and other organizations it is highly likely that a static web sites such as a work of Web-Art is highly likely to last as long as there is civilization. When you look at a web page, you could be the first (or conceivably the last [helloooo out there]) person to view that page. 2007-11-07 - added paragraph about crafts and transferring ownership 2007-10-13 - again many changes - first published