Encyclopedias have traditionally been regarded as second-rate sources of information, collections of summaries short on depth and authority, works you'd be embarrassed to cite in an academic paper or business presentation.

But, in comparison, with some of the other information available on the web, web encyclopedias don't look so bad after all. Instead of the rumors, hoaxes, exaggerations, and mistakes you sometimes surf across, encyclopedias, though far from perfect, are, for the most part, accurate and trustworthy.

Change is again rousing the world of encyclopedias. Microsoft, one of the early leaders of both CD-ROM and web encyclopedias, has just thrown in the towel, announcing in March the discontinuation of both versions of its Encarta encyclopedia. It plans to stop selling the software version by June and take down the web version in October.

Microsoft entered the encyclopedia space as it has typically entered other areas, by buying an existing product, in this case, nonexclusive rights to the Funk & Wagnalls encyclopedia. It incorporated Funk & Wagnalls, which at the time was an inexpensive encyclopedia sold largely through supermarkets, into the first edition on Encarta in 1993. Later, Microsoft bought Collier's Encyclopedia and New Merit Scholar's Encyclopedia and also incorporated them into Encarta, gradually improving it over the years.

To gain market share, Microsoft gave away its CD-ROM encyclopedia with many new computers, a strategy similar to those it has used in other areas. This seriously hurt Encyclopaedia Britannica, forcing its sale in 1996. Microsoft hasn't disclosed the reason for the discontinuation of Encarta, announcing that the "category of traditional encyclopedias and reference material has changed" and that "people today seek and consume information in considerably different ways."

It's clear, though, that Encarta, which was available through a paid subscription, has been done in by Wikipedia (www.wikipedia.org). This free, web-based encyclopedia is written and edited by readers, a strategy that perfectly fits the wide-open world of the web.

Since its inception in 2001, Wikipedia has grown explosively and now features nearly 3 million articles in English, far more than any competitor. The term "wiki" is a shortened form of "wiki wiki," which is a Hawaiian term for quick. Wikipedia makes seeking information a quick process; even when you do a Google search, another quick way of getting information, a Wikipedia article is often the first link that Google returns.

Wikipedia's formula of collaborative writing and editing has been so successful that Encyclopaedia Britannica (www.britannica.com), which remains in business under a new owner, announced this past January that the company would be accepting additions and edits to the web version from the public.

Encyclopaedia Britannica features about 125,000 articles and costs $69.95 per year. Unlike Wikipedia, it's written by known authors, either on-staff editors or outside experts. Its core of 700 Macropaedia articles is very thorough. Surprisingly, the accuracy of the two is nearly the same. In 2005, the scientific journal Nature published a study showing that in 42 randomly selected science articles, 162 mistakes appeared in Wikipedia compared to 123 in Encyclopaedia Britannica.

Wikipedia is otherwise far from perfect as well. The volunteers who write articles sometimes take excessive ownership of what they've contributed, deleting the changes, including corrections, that others make, despite the collaborative ideals behind the effort. Like the web in general, the egalitarian nature of Wikipedia favors the loudest voices over the most learned or informative.

What's more, as Wikipedia's own article on itself points out, because of its open nature, it has also been subjected to vandalism, though such attacks are usually corrected quickly.

One famous attack involved the article about John Seigenthaler Sr., an assistant to Attorney General Robert Kennedy in the early 1960s, in which an anonymous contributor suggested that Seigenthaler may have been directly involved in the assassinations of both John and Bobby Kennedy.

Other times, self-interest creates bias. Staff members of the U.S. congressmen have been caught changing the Wikipedia articles for their bosses, deleting references, for instance, to campaign pledges they failed to live up to.

Still, there's often very good information to be found through Wikipedia's populism. Just don't forget to take it with a grain of silicon. As with the internet in general, caveat lector, or let the reader beware. One good strategy, as with all information used for important purposes, is to vet information by seeking multiple sources.

The third major online encyclopedia today is the Columbia Encyclopedia, which, like Wikipedia, is free. It's available through Encyclopedia.com (www.encyclopedia.com), Dictionary.com (www.dictionary.com), and other sites.

Finally, there's still the library.