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A white sphere made of large jigsaw pieces, with letters from several alphabets shown on the pieces
Wikipedia wordmark
The logo of Wikipedia, a globe featuring glyphs from several writing systems[notes 1]
Type of site
Online encyclopedia
Available in 299 languages
Owner Wikimedia Foundation
Created by Jimmy Wales, Larry Sanger[1]
Slogan(s) The free encyclopedia that anyone can edit
Alexa rank Steady 5 (Global, November 2017)
Commercial No
Registration Optional[notes 2]
Users >469,324 active users[notes 3] and >70,435,391 registered users
Launched January 15, 2001; 16 years ago (2001-01-15)
Current status Active
Content license
CC Attribution / Share-Alike 3.0
Most text is also dual-licensed under GFDL; media licensing varies
Written in LAMP platform[2]
OCLC number 52075003

Wikipedia (/ˌwɪkɪˈpdiə/ (About this sound listen) WIK-i-PEE-dee-ə or /ˌwɪkiˈpdiə/ (About this sound listen) WIK-ee-PEE-dee-ə) is a free online encyclopedia with the aim to allow anyone to edit articles.[3] Wikipedia is the largest and most popular general reference work on the Internet,[4][5][6] and is ranked the fifth-most popular website.[7] Wikipedia is owned by the nonprofit Wikimedia Foundation.[8][9][10]

Wikipedia was launched on January 15, 2001, by Jimmy Wales and Larry Sanger.[11] Sanger coined its name,[12][13] a portmanteau of wiki[notes 4] and encyclopedia. There was only the English-language version initially, but similar versions in other languages quickly developed, which differ in content and in editing practices. With 5,515,466 articles,[notes 5] the English Wikipedia is the largest of the more than 290 Wikipedia encyclopedias. Overall, Wikipedia comprises more than 40 million articles in 299 different languages[15] and, as of February 2014, it had 18 billion page views and nearly 500 million unique visitors each month.[16] The Wikipedia logo contains an incomplete spherical puzzle with each piece having a different glyph on it.

As of March 2017, Wikipedia has about 40,000 high-quality articles, known as Featured Articles and Good Articles, that cover vital topics.[17][18] In 2005, Nature published a peer review comparing 42 science articles from Encyclopædia Britannica and Wikipedia, and found that Wikipedia's level of accuracy approached that of Encyclopædia Britannica.[19] Time magazine stated it was the remarkably open-door policy of allowing anyone to edit had made Wikipedia biggest and possibly the best encyclopedia in the World and it was testament to solely the vision of Jimmy Wales.[20]

Wikipedia has been criticized for allegedly exhibiting systemic bias, presenting a mixture of "truths, half truths, and some falsehoods",[21] and, in controversial topics, being subject to manipulation and spin.[22]


Jimmy Wales and Larry Sanger


Logo reading " the free encyclopedia" in blue with large initial "N"
Wikipedia originally developed from another encyclopedia project called Nupedia

Other collaborative online encyclopedias were attempted before Wikipedia, but none were successful.[23]

Wikipedia began as a complementary project for Nupedia, a free online English-language encyclopedia project whose articles were written by experts and reviewed under a formal process.[11] Nupedia was founded on March 9, 2000, under the ownership of Bomis, a web portal company. Its main figures were Jimmy Wales, the CEO of Bomis, and Larry Sanger, editor-in-chief for Nupedia and later Wikipedia. Nupedia was licensed initially under its own Nupedia Open Content License, switching to the GNU Free Documentation License before Wikipedia's founding at the urging of Richard Stallman.[24] Sanger and Wales founded Wikipedia.[25][26] While Wales is credited with defining the goal of making a publicly editable encyclopedia,[27][28] Sanger is credited with the strategy of using a wiki to reach that goal.[29] On January 10, 2001, Sanger proposed on the Nupedia mailing list to create a wiki as a "feeder" project for Nupedia.[30]

Wikipedia according to Simpleshow
External audio
The Great Book of Knowledge, Part 1, Ideas with Paul Kennedy, CBC, January 15, 2014

Launch and early growth

Wikipedia was launched on January 15, 2001, as a single English-language edition at,[31] and announced by Sanger on the Nupedia mailing list.[27] Wikipedia's policy of "neutral point-of-view"[32] was codified in its first months. Otherwise, there were relatively few rules initially and Wikipedia operated independently of Nupedia.[27] Originally, Bomis intended to make Wikipedia a business for profit.[33]

Wikipedia gained early contributors from Nupedia, Slashdot postings, and web search engine indexing. By August 8, 2001, Wikipedia had over 8,000 articles.[34] On September 25, 2001, Wikipedia had over 13,000 articles.[35] By the end of 2001, it had grown to approximately 20,000 articles and 18 language editions. It had reached 26 language editions by late 2002, 46 by the end of 2003, and 161 by the final days of 2004.[36] Nupedia and Wikipedia coexisted until the former's servers were taken down permanently in 2003, and its text was incorporated into Wikipedia. The English Wikipedia passed the mark of two million articles on September 9, 2007, making it the largest encyclopedia ever assembled, surpassing even the 1408 Yongle Encyclopedia, which had held the record for almost 600 years.[37]

Citing fears of commercial advertising and lack of control in Wikipedia, users of the Spanish Wikipedia forked from Wikipedia to create the Enciclopedia Libre in February 2002.[38] These moves encouraged Wales to announce that Wikipedia would not display advertisements, and to change Wikipedia's domain from to[39]

Though the English Wikipedia reached three million articles in August 2009, the growth of the edition, in terms of the numbers of articles and of contributors, appears to have peaked around early 2007.[40] Around 1,800 articles were added daily to the encyclopedia in 2006; by 2013 that average was roughly 800.[41] A team at the Palo Alto Research Center attributed this slowing of growth to the project's increasing exclusivity and resistance to change.[42] Others suggest that the growth is flattening naturally because articles that could be called "low-hanging fruit"—topics that clearly merit an article—have already been created and built up extensively.[43][44][45]

In November 2009, a researcher at the Rey Juan Carlos University in Madrid (Spain) found that the English Wikipedia had lost 49,000 editors during the first three months of 2009; in comparison, the project lost only 4,900 editors during the same period in 2008.[46][47] The Wall Street Journal cited the array of rules applied to editing and disputes related to such content among the reasons for this trend.[48] Wales disputed these claims in 2009, denying the decline and questioning the methodology of the study.[49] Two years later, in 2011, Wales acknowledged the presence of a slight decline, noting a decrease from "a little more than 36,000 writers" in June 2010 to 35,800 in June 2011. In the same interview, Wales also claimed the number of editors was "stable and sustainable".[50] A 2013 article titled "The Decline of Wikipedia" in MIT's Technology Review questioned this claim. The article revealed that since 2007, Wikipedia had lost a third of the volunteer editors who update and correct the online encyclopedia and those still there have focused increasingly on minutiae.[51] In July 2012, The Atlantic reported that the number of administrators is also in decline.[52] In the November 25, 2013, issue of New York magazine, Katherine Ward stated "Wikipedia, the sixth-most-used website, is facing an internal crisis".[53]

Wikipedia blackout protest against SOPA on January 18, 2012
A promotional video of the Wikimedia Foundation that encourages viewers to edit Wikipedia, mostly reviewing 2014 via Wikipedia content


In January 2007, Wikipedia entered for the first time the top-ten list of the most popular websites in the U.S., according to comScore Networks. With 42.9 million unique visitors, Wikipedia was ranked number 9, surpassing The New York Times (#10) and Apple (#11). This marked a significant increase over January 2006, when the rank was number 33, with Wikipedia receiving around 18.3 million unique visitors.[54] As of March 2015, Wikipedia has rank 5[7][55] among websites in terms of popularity according to Alexa Internet. In 2014, it received 8 billion pageviews every month.[56] On February 9, 2014, The New York Times reported that Wikipedia has 18 billion page views and nearly 500 million unique visitors a month, "according to the ratings firm comScore."[16]

On January 18, 2012, the English Wikipedia participated in a series of coordinated protests against two proposed laws in the United States Congress—the Stop Online Piracy Act (SOPA) and the PROTECT IP Act (PIPA)—by blacking out its pages for 24 hours.[57] More than 162 million people viewed the blackout explanation page that temporarily replaced Wikipedia content.[58][59]

Loveland and Reagle argue that, in process, Wikipedia follows a long tradition of historical encyclopedias that accumulated improvements piecemeal through "stigmergic accumulation".[60][61]

On January 20, 2014, Subodh Varma reporting for The Economic Times indicated that not only had Wikipedia's growth flattened but that it has "lost nearly 10 per cent of its page-views last year. That's a decline of about 2 billion between December 2012 and December 2013. Its most popular versions are leading the slide: page-views of the English Wikipedia declined by 12 per cent, those of German version slid by 17 per cent and the Japanese version lost 9 per cent."[62] Varma added that, "While Wikipedia's managers think that this could be due to errors in counting, other experts feel that Google's Knowledge Graphs project launched last year may be gobbling up Wikipedia users."[62] When contacted on this matter, Clay Shirky, associate professor at New York University and fellow at Harvard's Berkman Center for Internet and Security indicated that he suspected much of the page view decline was due to Knowledge Graphs, stating, "If you can get your question answered from the search page, you don't need to click [any further]."[62]

By the end of December 2016, Wikipedia was ranked fifth in the most popular websites globally.[63]

Number of English Wikipedia articles[64]
Wikipedia editors with >100 edits per month[64]


Differences between versions of an article are highlighted as shown

Unlike traditional encyclopedias,[which?] Wikipedia follows the procrastination principle[notes 6][65] regarding the security of its content.[65] It started almost entirely open—anyone could create articles, and any Wikipedia article could be edited by any reader, even those who did not have a Wikipedia account. Modifications to all articles would be published immediately. As a result, any article could contain inaccuracies such as errors, ideological biases, and nonsensical or irrelevant text.


Due to the increasing popularity of Wikipedia, popular editions, including the English version, have introduced editing restrictions in some cases. For instance, on the English Wikipedia and some other language editions, only registered users may create a new article.[66] On the English Wikipedia, among others, some particularly controversial, sensitive and/or vandalism-prone pages have been protected to some degree.[67][68] A frequently vandalized article can be semi-protected or extended confirmed protected, meaning that only autoconfirmed or extended confirmed editors are able to modify it.[69] A particularly contentious article may be locked so that only administrators are able to make changes.[70]

In certain cases, all editors are allowed to submit modifications, but review is required for some editors, depending on certain conditions. For example, the German Wikipedia maintains "stable versions" of articles,[71] which have passed certain reviews. Following protracted trials and community discussion, the English Wikipedia introduced the "pending changes" system in December 2012.[72] Under this system, new and unregistered users' edits to certain controversial or vandalism-prone articles are reviewed by established users before they are published.[73]

The editing interface of Wikipedia

Review of changes

Although changes are not systematically reviewed, the software that powers Wikipedia provides certain tools allowing anyone to review changes made by others. The "History" page of each article links to each revision.[notes 7][74] On most articles, anyone can undo others' changes by clicking a link on the article's history page. Anyone can view the latest changes to articles, and anyone may maintain a "watchlist" of articles that interest them so they can be notified of any changes. "New pages patrol" is a process whereby newly created articles are checked for obvious problems.[75]

In 2003, economics PhD student Andrea Ciffolilli argued that the low transaction costs of participating in a wiki create a catalyst for collaborative development, and that features such as allowing easy access to past versions of a page favor "creative construction" over "creative destruction".[76]


Any change or edit that manipulates content in a way that purposefully compromises the integrity of Wikipedia is considered vandalism. The most common and obvious types of vandalism include additions of obscenities and crude humor. Vandalism can also include advertising and other types of spam.[77] Sometimes editors commit vandalism by removing content or entirely blanking a given page. Less common types of vandalism, such as the deliberate addition of plausible but false information to an article, can be more difficult to detect. Vandals can introduce irrelevant formatting, modify page semantics such as the page's title or categorization, manipulate the underlying code of an article, or use images disruptively.[78]

White-haired elderly gentleman in suit and tie speaks at a podium.
American journalist John Seigenthaler (1927–2014), subject of the Seigenthaler incident

Obvious vandalism is generally easy to remove from Wikipedia articles; the median time to detect and fix vandalism is a few minutes.[79][80] However, some vandalism takes much longer to repair.[81]

In the Seigenthaler biography incident, an anonymous editor introduced false information into the biography of American political figure John Seigenthaler in May 2005. Seigenthaler was falsely presented as a suspect in the assassination of John F. Kennedy.[81] The article remained uncorrected for four months.[81] Seigenthaler, the founding editorial director of USA Today and founder of the Freedom Forum First Amendment Center at Vanderbilt University, called Wikipedia co-founder Jimmy Wales and asked whether he had any way of knowing who contributed the misinformation. Wales replied that he did not, although the perpetrator was eventually traced.[82][83] After the incident, Seigenthaler described Wikipedia as "a flawed and irresponsible research tool".[81] This incident led to policy changes at Wikipedia, specifically targeted at tightening up the verifiability of biographical articles of living people.[84]

Policies and laws

External video
Jimbo at Fosdem cropped.jpg
Wikimania, 60 Minutes, CBS, 20 minutes, April 5, 2015, co-founder Jimmy Wales at Fosdem

Content in Wikipedia is subject to the laws (in particular, copyright laws) of the United States and of the U.S. state of Virginia, where the majority of Wikipedia's servers are located. Beyond legal matters, the editorial principles of Wikipedia are embodied in the "five pillars" and in numerous policies and guidelines intended to appropriately shape content. Even these rules are stored in wiki form, and Wikipedia editors write and revise the website's policies and guidelines.[85] Editors can enforce these rules by deleting or modifying non-compliant material. Originally, rules on the non-English editions of Wikipedia were based on a translation of the rules for the English Wikipedia. They have since diverged to some extent.[71]

Content policies and guidelines

According to the rules on the English Wikipedia, each entry in Wikipedia must be about a topic that is encyclopedic and is not a dictionary entry or dictionary-like.[86] A topic should also meet Wikipedia's standards of "notability",[87] which generally means that the topic must have been covered in mainstream media or major academic journal sources that are independent of the article's subject. Further, Wikipedia intends to convey only knowledge that is already established and recognized.[88] It must not present original research. A claim that is likely to be challenged requires a reference to a reliable source. Among Wikipedia editors, this is often phrased as "verifiability, not truth" to express the idea that the readers, not the encyclopedia, are ultimately responsible for checking the truthfulness of the articles and making their own interpretations.[89] This can at times lead to the removal of information that is valid.[90] Finally, Wikipedia must not take sides.[91] All opinions and viewpoints, if attributable to external sources, must enjoy an appropriate share of coverage within an article.[92] This is known as neutral point of view (NPOV).


Wikipedia's initial anarchy integrated democratic and hierarchical elements over time.[93][94] An article is not considered to be owned by its creator or any other editor and is not vetted by any recognized authority.[95] Wikipedia's contributors avoid a tragedy of the commons by internalizing benefits. They do this by experiencing flow and identifying with and gaining status in the Wikipedia community.[96]


Editors in good standing in the community can run for one of many levels of volunteer stewardship: this begins with "administrator",[97][98] privileged users who can delete pages, prevent articles from being changed in case of vandalism or editorial disputes, and try to prevent certain persons from editing. Despite the name, administrators are not supposed to enjoy any special privilege in decision-making; instead, their powers are mostly limited to making edits that have project-wide effects and thus are disallowed to ordinary editors, and to implement restrictions intended to prevent certain persons from making disruptive edits (such as vandalism).[99][100]

Fewer editors become administrators than in years