KNOW IT ALL.

On March 1st, Wikipedia, the online interactive encyclopedia, hit the million-articles mark, with an entry on Jordanhill, a railway station in suburban Glasgow. Its author, Ewan MacDonald, posted a single sentence about the station at 11 P.M., local time; over the next twenty-four hours, the entry was edited more than four hundred times, by dozens of people. (Jordanhill happens to be the "1029th busiest station in the United Kingdom"; it "no longer has a staffed ticket counter.") The Encyclopaedia Britannica, which for more than two centuries has been considered the gold standard for reference works, has only a hundred and twenty thousand entries in its most comprehensive edition. Apparently, no traditional encyclopedia has ever suspected that someone might wonder about Sudoku or about prostitution in China. Or, for that matter, about Capgras delusion (the unnerving sensation that an impostor is sitting in for a close relative), the Boston molasses disaster, the Rhinoceros Party of Canada, Bill Gates's house, the forty-five-minute Anglo-Zanzibar War, or Islam in Iceland. Wikipedia includes fine entries on Kafka and the War of the Spanish Succession, and also a complete guide to the ships of the U.S. Navy, a definition of Philadelphia cheesesteak, a masterly page on Scrabble, a list of historical cats (celebrity cats, a cat millionaire, the first feline to circumnavigate Australia), a survey of invented expletives in fiction ("bippie," "cakesniffer," "furgle"), instructions for curing hiccups, and an article that describes, with schematic diagrams, how to build a stove from a discarded soda can. The how-to entries represent territory that the encyclopedia has not claimed since the eighteenth century. You could cure a toothache or make snowshoes using the original Britannica, of 1768-71. (You could also imbibe a lot of prejudice and superstition. The entry on Woman was just six words: "The female of man. See HOMO.") If you look up "coffee preparation" on Wikipedia, you will find your way, via the entry on Espresso, to a piece on types of espresso machines, which you will want to consult before buying. There is also a page on the site dedicated to "Errors in the Encyclopaedia Britannica that have been corrected in Wikipedia" (Stalin's birth date, the true inventor of the safety razor).

Because there are no physical limits on its size, Wikipedia can aspire to be all-inclusive. It is also perfectly configured to be current: there are detailed entries for each of the twelve finalists on this season's "American Idol," and the article on the "2006 Israel-Lebanon Conflict" has been edited more than four thousand times since it was created, on July 12th, six hours after Hezbollah militants ignited the hostilities by kidnapping two Israeli soldiers. Wikipedia, which was launched in 2001, is now the seventeenth-most-popular site on the Internet, generating more traffic daily than MSNBC.com and the online versions of the Times and the Wall Street Journal combined. The number of visitors has been doubling every four months; the site receives as many as fourteen thousand hits per second. Wikipedia functions as a filter for vast amounts of information online, and it could be said that Google owes the site for tidying up the neighborhood. But the search engine is amply repaying its debt: because Wikipedia pages contain so many links to other entries on the site, and are so frequently updated, they enjoy an enviably high page rank.

The site has achieved this prominence largely without paid staff or revenue. It has five employees in addition to Jimmy Wales, Wikipedia's thirty-nine-year-old founder, and it carries no advertising. In 2003, Wikipedia became a nonprofit organization; it meets most of its budget, of seven hundred and fifty thousand dollars, with donations, the bulk of them contributions of twenty dollars or less. Wales says that he is on a mission to "distribute a free encyclopedia to every single person on the planet in their own language," and to an astonishing degree he is succeeding. Anyone with Internet access can create a Wikipedia entry or edit an existing one. The site currently exists in more than two hundred languages and has hundreds of thousands of contributors around the world. Wales is at the forefront of a revolution in knowledge gathering: he has marshalled an army of volunteers who believe that, working collaboratively, they can produce an encyclopedia that is as good as any written by experts, and with an unprecedented range.

Wikipedia is an online community devoted not to last night's party or to next season's iPod but to a higher good. It is also no more immune to human nature than any other utopian project. Pettiness, idiocy, and vulgarity are regular features of the site. Nothing about high-minded collaboration guarantees accuracy, and open editing invites abuse. Senators and congressmen have been caught tampering with their entries; the entire House of Representatives has been banned from Wikipedia several times. (It is not subtle to change Senator Robert Byrd's age from eighty-eight to a hundred and eighty. It is subtler to sanitize one's voting record in order to distance oneself from an unpopular President, or to delete broken campaign promises.) Curiously, though, mob rule has not led to chaos. Wikipedia, which began as an experiment in unfettered democracy, has sprouted policies and ...