Wikipedia is a Web-based, free-content encyclopedia, which is written collaboratively by volunteers. It consists of 195 independent language editions sponsored by the non-profit Wikimedia Foundation. Entries on traditional encyclopedic topics exist alongside those on almanac, gazetteer and current events topics. Its purpose is to create and distribute, worldwide, a free encyclopedia in as many languages as possible. Wikipedia is one of the most popular reference sites on the Web,^[1]   receiving around 50 million hits per day.

Wikipedia contains approximately 1.5 million articles, more than 500,000 of which are in its English language edition. It began as a complement to the expert-written Nupedia on 15 January 2001. Having steadily risen in popularity,^[2] it has spawned several conceptually related sister projects such as Wiktionary, Wikibooks and Wikinews. Its articles are edited by volunteers in wiki fashion, meaning articles are subject to change by nearly anyone. Wikipedia's volunteers enforce a policy of "neutral point of view." Under this, the views presented by notable persons or literature are summarized without attempting to determine an objective truth. By its open nature, vandalism and inaccuracy are problems in Wikipedia.

Wikipedia's status as a reference work has been controversial. It has received praise for being free, editable, and covering a wide range of topics. It has been criticized for lack of authority when compared with a traditional encyclopedia, systemic bias, and for deficiencies in traditional encyclopedic topics. Its articles have been cited by the mass media and academia. Wikipedia's articles are available under the GNU Free Documentation License.