
Since the launch of Wikipedia in January 2001, a number of controversies have occurred. Wikipedia's open nature, in which anyone can edit most articles, has led to various concerns, such as the quality of writing, the amount of vandalism, and the accuracy of information on the project. The media have covered a number of controversial events and scandals related to Wikipedia and its parent organization, the Wikimedia Foundation (WMF). Common subjects of coverage include articles containing false information, public figures and corporations editing articles for which they have a serious conflict of interest, paid Wikipedia editing and hostile interactions between Wikipedia editors and public figures.

The Henryk Batuta hoax was a hoax perpetrated on the Polish Wikipedia from November 2004 to February 2006, the main element of which was a biographical article about a nonexistent socialist revolutionary, Henrik Batuta.

Over a three-day period from June 22 to 24, 2007, Chris Benoit, a 40-year-old French-Canadian professional wrestler employed by World Wrestling Entertainment (WWE) and living in Fayetteville, Georgia, killed his wife Nancy Benoit and their 7-year-old son, Daniel, before hanging himself. Autopsy results showed that Benoit's wife was murdered first as she was bound at the feet and wrists and died of asphyxiation on the night of June 22. On June 25, Nancy was found wrapped in a towel with blood under her head, although Fayette County District Attorney Scott Ballard reported no other signs of a struggle.

The reliability of Wikipedia concerns the validity, verifiability, and veracity of Wikipedia and its user-generated editing model, particularly its English-language edition. It is written and edited by volunteer editors who generate online content with the editorial oversight of other volunteer editors via community-generated policies and guidelines. Wikipedia carries the general disclaimer that it can be "edited by anyone at any time" and maintains an inclusion threshold of "verifiability, not truth." This editing model is highly concentrated as 77% of all articles are written by 1% of its editors, a majority of whom are anonymous. The reliability of the project has been tested statistically, through comparative review, analysis of the historical patterns, and strengths and weaknesses inherent in its editing process. The online encyclopedia has been criticized for its factual reliability, principally regarding its content, presentation, and editorial processes. Studies and surveys attempting to gauge the reliability of Wikipedia have been mixed, with findings varied and inconsistent.

The Croatian Wikipedia is the Croatian version of Wikipedia, the free encyclopedia, started on February 16, 2003. This version has 209,591 articles and a total of 6.03 million edits have been made. It has 260,583 registered user accounts, out of which 514 are active, and 15 administrators.

The Croatian Wikipedia is the Croatian version of Wikipedia, the free encyclopedia, started on February 16, 2003. This version has 209,591 articles and a total of 6.03 million edits have been made. It has 260,583 registered user accounts, out of which 514 are active, and 15 administrators.

Enciclopedia Libre Universal en Español is a Spanish-language wiki-based online encyclopedia, released under the Creative Commons Attribution-ShareAlike License 3.0. It uses the MediaWiki software. It started as a fork of the Spanish Wikipedia.

The Essjay controversy centered on Ryan Jordan, a Wikipedia editor who went by the username Essjay. On Wikipedia, he falsely presented himself as a university professor of religion. He was active from 2005 to 2008, and was elected to top positions of trust by the community, including the rank of administrator and arbitration committee member. In July 2006, The New Yorker published an article about "Essjay", and mentioned that he was a university professor of religion. The New Yorker later acknowledged it did not know his real name. The controversy came to involve Wikipedia co-founder Jimmy Wales who, after initially defending Jordan, eventually asked for his resignation in March 2007.

Gibraltarpedia is a project by the Government of Gibraltar, a British Overseas Territory in the south of the Iberian Peninsula, to improve coverage of Gibraltar-related topics on Wikipedia. It builds on Monmouthpedia, an earlier project along similar lines linking Wikipedia and the town of Monmouth in South Wales. The Gibraltarpedia project was announced in July 2012 by the Government of Gibraltar.

The Indian Institute of Planning and Management (IIPM) was an unaccredited institute headquartered in New Delhi, which previously had 18 branches across India. The institute has been widely criticized for false advertisements and fraudulent practices. After several controversies, the school's Honorary Dean Arindam Chaudhuri decided to shut down all campuses across India, except the one in Delhi. Founded in 1973, the institute used to offer undergraduate, postgraduate and doctoral programmes in national economic planning and entrepreneurship, and international and fellowship programmes. Its executive education programmes include non-credit courses and visits to foreign business schools. IIPM is not accredited by UGC or All India Council for Technical Education (AICTE), and is not affiliated with the public Indian Institutes of Management.

On 5 December 2008, the Internet Watch Foundation (IWF), a British watchdog group, blacklisted content on the English Wikipedia related to Scorpions' 1976 studio album Virgin Killer, due to the presence of its controversial cover artwork, depicting a young girl posing nude, with a faux shattered-glass effect obscuring her genitalia. The image was deemed to be "potentially illegal content" under English law which forbids the possession or creation of indecent photographs of children. The IWF's blacklist are used in web filtering systems such as Cleanfeed.

Jar'Edo Wens was a deliberately fictitious Wikipedia article which existed for almost 10 years before being spotted in November 2014 and deleted in March 2015. At the time, it was the longest-lasting hoax article discovered in the history of Wikipedia.

Lsjbot is an automated Wikipedia article-creating program, or Wikipedia bot, developed by Sverker Johansson for the Swedish Wikipedia. The bot primarily focuses on articles about living organisms and geographical entities.

Alan Mcilwraith is a Scottish former call centre worker from Glasgow who was exposed as a military impostor by a tabloid newspaper after he passed himself off as a much-decorated British Army officer.

The monkey selfie copyright dispute is a series of disputes about the copyright status of selfies taken by Celebes crested macaques using equipment belonging to the British nature photographer David Slater. The disputes involve Wikimedia Commons and the blog Techdirt, which have hosted the images following their publication in newspapers in July 2011 over Slater's objections that he holds the copyright, and People for the Ethical Treatment of Animals (PETA), who have argued that the macaque should be assigned the copyright.

MyWikiBiz is a wiki directory that allows people and enterprises to write about themselves. The brand began as a service creating Wikipedia articles for paying corporations.

In July 2009, lawyers representing the National Portrait Gallery of London (NPG) sent an email letter warning of possible legal action for alleged copyright infringement to Derrick Coetzee, an editor/administrator of the free content multimedia repository Wikimedia Commons, hosted by the Wikimedia Foundation.

Clarice Evone Phelps is an American nuclear chemist researching the processing of radioactive transuranic elements at the U.S. Department of Energy's Oak Ridge National Laboratory (ORNL). She was part of ORNL's team that collaborated with the Joint Institute for Nuclear Research to discover tennessine. The International Union of Pure and Applied Chemistry, recognizes her as the first African-American woman to be involved with the discovery of a chemical element. Phelps was formerly in the US Navy Nuclear Power Program. At ORNL, Phelps manages programs in the Department of Energy's Isotope & Fuel Cycle Technology Division investigating industrial uses of nickel-63 and selenium-75.

The Scots Wikipedia is the Scots-language edition of the free online encyclopedia, Wikipedia. It was established on 23 June 2005, and it first reached 1,000 articles in February 2006, and 5,000 articles in November 2010. As of August 2021, it has about 40,000 articles. The Scots Wikipedia is one of eight Wikipedias written in an Anglic language or English-based pidgin/creole, the others being the English Wikipedia, the Simple English Wikipedia, the Old English Wikipedia, the Pitkern-Norfuk Wikipedia, the Tok Pisin Wikipedia, the Jamaican Patois Wikipedia, and the Sranan Tongo Wikipedia.

Wiki-PR is a consulting firm that formerly marketed the ability to edit Wikipedia by "...directly edit[ing] your page using our network of established Wikipedia editors and admin[s]".

In May 2005, an unregistered editor posted a hoax article onto Wikipedia about journalist John Seigenthaler. The article falsely stated that Seigenthaler had been a suspect in the assassinations of U.S. President John F. Kennedy and U.S. Attorney General Robert F. Kennedy.