This is a list of notable conspiracy theories. Many conspiracy theories relate to supposed clandestine government plans and elaborate murder plots. They usually deny consensus opinion and cannot be proven using historical or scientific methods, and are not to be confused with research concerning verified conspiracies, such as Germany's pretense for invading Poland in World War II.
In principle, conspiracy theories might not always be false, and their validity depends on evidence as for any theory. However, they are often implausible prima facie due to their convoluted and all-encompassing nature. Conspiracy theories tend to be internally consistent and correlate with each other; they are generally designed to resist falsification either by evidence against them or a lack of evidence for them.
Psychologists sometimes attribute proclivities toward conspiracy theories to a number of psychopathological conditions such as paranoia, schizotypy, narcissism, and insecure attachment, or to a form of cognitive bias called "illusory pattern perception". However, the current scientific consensus holds that most conspiracy theorists are not pathological, but merely exaggerate certain cognitive tendencies that are universal in the human brain and probably have deep evolutionary origins, such as natural inclinations towards anxiety and agent detection.
Alternative history theories
False historical timelines
Some theories claim that the dates of historical events have been deliberately distorted. These include the phantom time hypothesis of German conspiracy theorist Heribert Illig, who in 1991 published an allegation that 297 years had been added to the calendar by establishment figures such as Pope Sylvester II in order to position themselves at the millennium.
A comparable theory, new chronology, is associated with Russian theorist Anatoly Fomenko, who holds that history is many centuries shorter than widely believed, numerous historical documents have been fabricated, and legitimate documents destroyed, all for political ends. Adherents have included chess grandmaster Garry Kasparov.
Pre-Māori settlement of New Zealand
New Zealand was first inhabited by indigenous Māori who arrived from Polynesia in the 14th century AD.
The Moriori were a group of Polynesians who left the New Zealand mainland for the Chatham Islands in 1500 AD. Some historians in the 1800s proposed that the Moriori were a pre-Māori civilization which some theorists still believe to be true despite it being disproven.
Māori mythology tells of races such as the patupaiarehe living in New Zealand before Māori. Other conspiracy theorists have suggested New Zealand was colonised by groups like the Chinese and Spanish.
Proponents of these theories may rely on pseudo-archaeological findings. Findings of Kiore rat fossils found beneath tephra of the Taupō Volcanic eruption were unable to be replicated elsewhere. Others have interpreted natural geological rock formations such as the Kaimanawa Wall as pyramids.
Tartaria
Another claim is that world governments have hidden evidence for an advanced worldwide civilization with access to free energy and partially populated by giants called Tartaria, which was destroyed in the 1800s by a great "mud flood" cataclysm, causing its remains to be buried.
Aviation Numerous conspiracy theories pertain to air travel and aircraft. Incidents such as the 1955 bombing of the Kashmir Princess, the 1985 Arrow Air Flight 1285 crash, the 1986 Mozambican Tupolev Tu-134 crash, the 1987 Helderberg disaster, the 1988 bombing of Pan Am Flight 103 and the 1994 Mull of Kintyre helicopter crash as well as various aircraft technologies and alleged sightings, have all spawned theories of foul play that deviate from official verdicts.
Black helicopters
This conspiracy theory emerged in the US in the 1960s. The John Birch Society originally promoted it, asserting that a United Nations force would soon arrive in black helicopters to bring the US under UN control. A similar theory concerning so-called "phantom helicopters" appeared in the UK in the 1970s. The theory re-emerged in the 1990s during the presidency of Bill Clinton, and was "energetically" promoted by writer Jim Keith in his book Black Helicopters Over America. By the 2000s, the term "black helicopters" became a shorthand for anti-government conspiracy theories that "stretch the bounds of credulity", such as those espoused by militia groups and a number of guests of talk show host Glenn Beck.
Chemtrails
Also known as SLAP (Secret Large-scale Atmospheric Program), this theory alleges that water condensation trails ("contrails") from aircraft consist of chemical or biological agents, or contain a supposedly toxic mix of aluminum, strontium and barium, under secret government policies. An estimated 17% of people globally believe the theory to be true or partly true. In 2016, the Carnegie Institution for Science published the first-ever peer-reviewed study of the chemtrail theory; 76 out of 77 participating atmospheric chemists and geochemists stated that they had seen no evidence to support the chemtrail theory or stated that chemtrail theorists rely on poor sampling.
Korean Air Lines Flight 007 The destruction of Korean Air Lines Flight 007 by Soviet jets in 1983 has long drawn the interest of conspiracy theorists. The theories range from allegations of a planned espionage mission, to a US government cover-up, to the consumption of the passengers' remains by giant crabs.Izvestia, 8 February 1991, pg. 7
Malaysia Airlines Flight MH370
The disappearance of Malaysia Airlines Flight 370 in southeast Asia in March 2014 has prompted many theories. One theory suggests that this plane was hidden away and reintroduced as Flight MH17 later the same year in order to be shot down over Ukraine for political purposes. American conspiracy theorist James H. Fetzer has placed responsibility for the disappearance with the then Israeli prime minister Benjamin Netanyahu. Historian Norman Davies has promoted the conspiracy theory that hackers remotely took over a Boeing Uninterruptible Autopilot, supposedly installed on board, remotely piloting the aircraft to Antarctica.
Malaysia Airlines Flight MH17 Malaysia Airlines Flight 17 was shot down over Ukraine in July 2014. This event has spawned numerous alternative theories. These variously include allegations that it was secretly Flight MH370, that the plane was actually shot down by the Ukrainian Air Force to frame Russia, that it was part of a conspiracy to conceal the "truth" about HIV (seven disease specialists were on board), or that the Illuminati or Israel was responsible.
Business and industry
Deepwater Horizon Multiple conspiracy theories pertain to a fatal oil-rig industrial accident in 2010 in the Gulf of Mexico, alleging sabotage by those seeking to promote environmentalism, or a strike by North Korean or Russian submarines. Elements of such theories had been suggested or promoted by US radio host Rush Limbaugh.
New Coke
A theory claims that the Coca-Cola Company intentionally changed to an inferior formula with New Coke, with the intent either of driving up demand for the original product or permitting the reintroduction of the original with a new formula using cheaper ingredients. Coca-Cola president Donald Keough rebutted this charge: "The truth is, we're not that dumb, and we're not that smart."
Deaths and disappearances
Death of Nero In ancient times, widespread conspiracy theories were circulated pertaining to the death of the Roman emperor Nero, who killed himself in 68 AD. Some of these theories claimed that Nero had actually faked his death and was secretly still alive, but in hiding, plotting to reestablish his reign. In most of these stories, he was said to have fled to the East, where he was still influential. Other theories held that Nero would return from the dead to retake his throne. Many early Christians feared Nero's return to resume his vicious anti-Christian persecutions. The Book of Revelation may allude to these conspiracy theories in its description of the slaughtered head returned to life.
John F. Kennedy assassination
Multiple conspiracy theories concerning the assassination of John F. Kennedy in 1963 have emerged. Vincent Bugliosi estimated that more than 1,000 books had been written about the Kennedy assassination, at least ninety percent of which are works supporting the view that there was a conspiracy. As a result of this, the Kennedy assassination has been described as "the mother of all conspiracies". The countless individuals and organizations that have been accused of involvement in the Kennedy assassination include the CIA, the Mafia, sitting Vice President Lyndon B. Johnson, Cuban Prime Minister Fidel Castro, the KGB, or even some combination thereof. It is also frequently asserted that the United States federal government intentionally covered up crucial information in the aftermath of the assassination to prevent the conspiracy from being discovered.
Charlie Kirk assassination
Numerous conspiracy theories about the assassination of Charlie Kirk were posted online. Political consultant Roger Stone said the attack appeared to have been "a professional hit either by a nation state, rogue elements of our own government or a terrorist organization". One theory, promulgated by Russian state media RT, centered on people standing near Kirk, who were purported to have made "unusual gestures" before he was killed. Several senior Russian officials, including former president Dmitry Medvedev and Kremlin special envoy Kirill Dmitriev, speculated on social media about a connection between Kirk's killing and United States support for Ukraine because Kirk had been a critic of Western financial and political support for Ukraine in its conflict with Russia.
Other conspiracy theories include claims that Israel was involved. Many sources, including Israeli media, have stated that these theories are rooted in antisemitism. Some commentators attempted to link the event to the Israeli Mossad and to Kirk's comments about the Epstein files, and Maram Susli resurfaced an August 2025 post by an Infowars host who stated that Kirk believed "Israel will kill [him] if he turns against them". Tucker Carlson was accused by some pro-Israel groups in the United States of making antisemitic comments at the service for Kirk by suggesting he supported the conspiracy theory that Jews or Israel were responsible for the assassination. Carlson said that Kirk's assassination reminded him of the death of Jesus Christ, whom he said was killed by powerful people for telling the truth. Israeli prime minister Benjamin Netanyahu rejected the theories, calling them "insane" and issuing multiple video messages claiming no Israeli government involvement in the assassination.
Disappearance of Harold Holt
At approximately 12:20 pm on 17 December 1967, then-Prime Minister of Australia Harold Holt disappeared while swimming at Cheviot Beach, near the town of Portsea in Victoria. While it is presumed that Holt drowned, the topic is still described as one of the biggest unsolved mysteries in Australian history and has spawned many conspiracy theories. The conspiracy theories have been widely criticised by the public and by members of Holt's own family.