Wikipedia is a multilingual Web-based free-content encyclopedia wiki service. Wikipedia is written collaboratively by volunteers, allowing most articles to be changed by anyone with access to a web browser. The project began on January 15, 2001, as a complement to the expert-written Nupedia and is now operated by the non-profit Wikimedia Foundation. Wikipedia has more than 3,210,000 articles, including more than 950,000 in the English-language version, and as of January 2006 it has more than 863,000 registered users. Since its inception, Wikipedia has steadily risen in popularity, and its success has spawned several sister projects. There has, however, been controversy over its reliability.
Wikipedia is regularly cited in the mass media and academia, sometimes critically, and sometimes to praise it for its free distribution, constant editing, and diverse coverage, not to mention its multilingual dimensions. It is often cited not as a subject but as a source on other subjects. Editors are encouraged to uphold a policy of “neutral point of view” under which notable perspectives are summarized without an attempt to determine an objective truth. Wikipedia’s status as a reference work has been controversial since its open nature allows vandalism, inaccuracy, inconsistency, uneven quality, and unsubstantiated opinions. It has also been criticised for systemic bias, preference of consensus to credentials, and a perceived lack of accountability and authority when compared with traditional encyclopedias. But the scope and detail of its articles, as well as its constant updates, have made it a useful reference source for millions.
There are over 200 language editions of Wikipedia, around 100 of which are active. Twelve editions have more than 50,000 articles each: English, German, French, Japanese, Polish, Italian, Swedish, Dutch, Portuguese, Spanish, Chinese and Russian. Its German-language edition has been distributed on DVD-ROM, and there are proposals for an English DVD/paper edition. Many of its other editions are mirrored or have been forked by websites.