Jimmy Wales vividly remembers the green-bindered World Book Encyclopedia of his youth. His parents kept the 22-volume set in the living room of their Huntsville, Ala., home. Each year, as the encyclopedia got progressively out of date, World Book mailed updates along with stickers to put next to obsolete articles. Wales recalls poring through the old and new versions and attaching the stickers while analyzing each advancement in fields like space exploration. "I read it voraciously," he says. "I really loved it."

Today, Wales, 38, a computer programmer in St. Petersburg, Fla., is trying to make the entire concept of a printed reference book obsolete. Three years ago he created the Wikipedia (, a free online encyclopedia that draws articles not from a sequestered brain trust of academics but from the great unwashed: thousands of Internet users around the world who freely add to and edit the site. It's one part reference tool, one part fascinating social experiment. Visitors can create their own entries or change existing ones, contributing their bookish wisdom and, yes, sometimes mistakes or outright misinformation as well. For Wales, running the rapidly growing reference work has also become an immersive, full-time job. Wikipedia just roared past 1 million total articles (300,000 in English, the rest mostly in 40 other languages), making it the world's largest encyclopedia--three times the size of the 233-year-old Britannica. Some professional researchers even use it, though cautiously. "It's a good resource for the casual user," says Stephen Bolhafner, a researcher at the St. Louis Post-Dispatch. "I use it as a second or third source to confirm something."

Wales first tried to rewrite the rules of the reference-book business five years ago with a free online encyclopedia called Nupedia. Anyone could submit articles, but they were vetted in a seven-step review process. After investing thousands of his own dollars and publishing only 24 articles, Wales reconsidered. He scrapped the review process and began using a popular kind of online Web site called a "wiki," which allows its readers to change the content. ("Wiki" is a Hawaiian word for fast.) Wales took inspiration from the free-software movement, in which programmers worldwide contribute to code, building on each other's work and, in the end, produce professional-grade products.

But if an encyclopedia is only as good as its reputation for accuracy, Wikipedia has an inherent problem. On any entry, any user can slip a humdinger into the public record, intentionally or otherwise. A disclaimer on says it "can't guarantee the validity of the information found here." Still, as it's grown, the enthusiasm of its contributors provides a natural check on inaccuracies. Every month, 1,900 users make at least 100 edits each to the site. For no pay, these "Wikipediaholics" typically monitor every change made to the topics that interest them (which they track on "watchlists" that automatically alert them to updates). They can quickly fix problems if someone vandalizes an entry or violates the site's pledge of neutrality.

Often, things can get even more complicated. Conflicts regularly occur over the language on sensitive topics, such as the details of John Kerry's war record. Wales set up community discussion boards and a formal mediation system to settle disputes. "A collaborative encyclopedia sounds like a crazy idea, but it naturally controls itself," says Angela Beesley, a volunteer from Essex, England, and a self-confessed Wikipedia addict who monitors the accuracy of more than 1,000 entries.

Wales has registered the Wikipedia Foundation as a nonprofit in Florida. He has no full-time employees and no formal funding like venture capital, but this year he's raised $100,000 in small donations from Wikipedia's fans that will pay for the servers that host the site. He's also expanding into projects like the Wiktionary (a dictionary and thesaurus), Wikibooks (textbooks and manuals) and Wikiquote (quotations). The goal: to give "every single person free access to the sum of all human knowledge." To achieve that, he doesn't even have to send out stickers.