Jimmy Wales and Larry Sanger
Wikipedia originally developed from another encyclopedia project called
Other collaborative online encyclopedias were attempted before Wikipedia, but none were as successful.
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.
 Nupedia was founded on March 9, 2000, under the ownership of
web portal company. Its main figures were
Jimmy Wales, the CEO of Bomis, and
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
 Sanger and Wales founded Wikipedia.
 While Wales is credited with defining the goal of making a publicly editable encyclopedia,
 Sanger is credited with the strategy of using a
wiki to reach that goal.
 On January 10, 2001, Sanger proposed on the Nupedia
mailing list to create a wiki as a "feeder" project for Nupedia.
Launch and early growth
Wikipedia was launched on January 15, 2001, as a single English-language edition at www.wikipedia.com,
 and announced by Sanger on the Nupedia mailing list.
 Wikipedia's policy of "neutral point-of-view"
 was codified in its first months. Otherwise, there were relatively few rules initially and Wikipedia operated independently of Nupedia.
 Originally, Bomis intended to make Wikipedia a business for profit.
Wikipedia gained early contributors from Nupedia,
Slashdot postings, and
web search engine indexing. By August 8, 2001, Wikipedia had over 8,000 articles.
 On September 25, 2001, Wikipedia had over 13,000 articles.
 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.
 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.
Citing fears of commercial advertising and lack of control in Wikipedia, users of the
forked from Wikipedia to create the
Enciclopedia Libre in February 2002.
 These moves encouraged Wales to announce that Wikipedia would not display advertisements, and to change Wikipedia's domain from wikipedia.com to wikipedia.org.
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.
 Around 1,800 articles were added daily to the encyclopedia in 2006; by 2013 that average was roughly 800.
 A team at the
Palo Alto Research Center attributed this slowing of growth to the project's increasing exclusivity and resistance to change.
 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.
In November 2009, a researcher at the
Rey Juan Carlos University in
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.
 The Wall Street Journal cited the array of rules applied to editing and disputes related to such content among the reasons for this trend.
 Wales disputed these claims in 2009, denying the decline and questioning the methodology of the study.
 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".
 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.
 In July 2012,
The Atlantic reported that the number of administrators is also in decline.
 In the November 25, 2013, issue of
New York magazine, Katherine Ward stated "Wikipedia, the sixth-most-used website, is facing an internal crisis".
Wikipedia blackout protest against
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.
 As of March 2015 , Wikipedia has rank 5
 among websites in terms of popularity according to
Alexa Internet. In 2014, it received 8 billion pageviews every month.
 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."
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.
 More than 162 million people viewed the blackout explanation page that temporarily replaced Wikipedia content.
Loveland and Reagle argue that, in process, Wikipedia follows a long tradition of historical encyclopedias that accumulated improvements piecemeal through "
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."
 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."
 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]."
By the end of December 2016, Wikipedia was ranked fifth in the most popular websites globally.