Since the September 11 attacks, doubts have been raised about the mainstream account of events. There have been a number of 9/11 conspiracy theories with some suggesting that Israel was involved in the attacks and that members of the U.S. government may have deliberately covered-up and falsified events, in order to hide negligence, complicity, or even having been the perpetrator of the attacks.

A number of 9/11 opinion polls have been carried out to assess the prevalence of various opinions and views about questions related to the attacks, both in the United States and in other countries.

The size, form and quality of polls naturally vary considerably, as does the range and specificity of questions asked. They range from large, formal polls such as those conducted by Zogby International, to smaller, informal polls of limited scope, such as internet polls. The questions here relate specifically to doubts about the mainstream account, and in all cases were part of a group of questions dealing with wider issues, usually of a political nature.

World opinion polls

A poll taken by WorldPublicOpinion.org, a collaborative project of research centers in various countries managed by the Program on International Policy Attitudes at the University of Maryland, College Park, polled 16,063 people in 17 nations outside of the United States during the summer of 2008. They found that majorities in only 9 of the 17 countries believe al-Qaeda carried out the attacks.

45 percent of those surveyed said al-Qaeda was responsible, 15 percent said the U.S. government, 7 percent said Israel and 7 percent said some other perpetrator. One in four people said they did not know who was behind the attacks.

The summary of the poll noted that "Though people with greater education generally have greater exposure to news, those with greater education are only slightly more likely to attribute 9/11 to al Qaeda." Steven Kull, director of WorldPublicOpinion.org, commented "It does not appear that these beliefs can simply be attributed to a lack of exposure to information." Of those who said the United States was the perpetrator, Kull says many believe it was an attempt to justify an impending U.S. invasion of Iraq.

National opinion polls

United States

Zogby International

The polls that have received the most widespread media attention are those conducted by Zogby International. The Zogby polls have been sponsored by organizations within the 9/11 Truth Movement including 911truth.org.

The first one was conducted in late August 2004 on 808 randomly selected residents of New York State. It found that 49 percent of New York City residents and 41 percent of New York state citizens believe individuals within the U.S. government "knew in advance that attacks were planned on or around September 11, 2001, and that they consciously failed to act." The margin of error for this poll was 3.5 percent.

The second major Zogby poll on 9/11 was conducted in May 2006. It was a telephone interview of 1,200 randomly selected adults from across the United States, consisting of 81 questions, with a 2.9 percent margin of error. Some of the questions asked include the following:

"Some people believe that the US government and its 9/11 Commission concealed or refused to investigate critical evidence that contradicts their official explanation of the September 11th attacks, saying there has been a cover-up. Others say that the 9/11 Commission was a bi-partisan group of honest and well-respected people and that there is no reason they would want to cover-up anything. Who are you more likely to agree with?"

Responses: 48% No Cover-up / 42% Cover-up / 10% Not sure

"World Trade Center Building 7 is the 47-story skyscraper that was not hit by any planes during the September 11th attacks, but still totally collapsed later the same day. This collapse was not investigated by the 9/11 Commission. Are you aware of this skyscraper's collapse, and if so do you believe that the Commission should have also investigated it? Or do you believe that the Commission was right to only investigate the collapse of the buildings which were directly hit by airplanes?"

Responses: 43% Not Aware / 38% Aware - should have investigated it / 14% Aware - right not to investigate it / 5% Not Sure

"Some people say that so many unanswered questions about 9/11 remain that Congress or an International Tribunal should re-investigate the attacks, including whether any US government officials consciously allowed or helped facilitate their success. Other people say the 9/11 attacks were thoroughly investigated and that any speculation about US government involvement is nonsense. Who are you more likely to agree with?"

Responses: 47% Attacks were thoroughly investigated / 45% Reinvestigate the attacks / 8% Not Sure

The third major Zogby poll regarding 9/11 was conducted in August 2007. It was a telephone interview with a target of 1,000 interviews with randomly selected adults from across the United States, consisting of 71 questions, with a 3.1 percent margin of error.

The results of the 2007 August poll indicate that 51 percent of Americans want the United States Congress to probe President George W. Bush and Vice President Dick Cheney regarding the 9/11 attacks and over 30 percent of those polled seek immediate impeachment. While only 32 percent seek immediate impeachment of Bush and/or Cheney based on their personal knowledge, many citizens appear eager for clear exposure of the facts.

In addition, the poll also found that two-thirds (67 percent) of Americans say the 9/11 Commission should have investigated the collapse of World Trade Center Building 7. Only 4.8 percent of the respondents agreed that members of the U.S. government "actively planned or assisted some aspects of the attack."

Newsweek magazine polls

The Newsweek magazine poll "What America Knows," conducted by Princeton Survey Research Associates International, regularly asks American citizens a wide range of questions relating to world events both past and present, and a number of more trivial questions of general knowledge. Poll conducted by Princeton Survey Research Associates International. On five occasions the following question has been asked:

"Do you think Saddam Hussein's regime in Iraq was directly involved in planning, financing, or carrying out the terrorist attacks of September 11th, 2001?"

September 2003 responses: 47% Yes, 37% No, 16% not sure. January 2004 responses: 49% Yes, 39% No, 12% not sure. September 2004 responses: 42% Yes, 44% No, 14% not sure. October 2004 responses: 36% Yes, 51% No, 13% not sure. June 2007 responses: 41% Yes, 50% No, 9% not sure.

The New York Times / CBS News polls

The first 9/11 poll carried out by The New York Times and CBS News was conducted in May 2002. The same 9/11-related question was asked again in April 2004 and October 2006. The 2002 and 2006 polls were apparently published for the first time not by the NYT or CBS, but by polling researcher Angus Reid Public Opinion. The 2004 NYT/CBS poll is available at nytimes.com (Question 77).

The 2004 poll was conducted by telephone with 1,042 adults nationwide in the United States, with a 3 percent margin of error. The 2006 poll was conducted by telephone on 983 randomly selected citizens of the United States, with a 4 percent margin of error. One of the questions was the following:

"When it comes to what they knew prior to September 11th, 2001, about possible terrorist attacks against the United States, do you think members of the Bush Administration are telling the truth, are mostly telling the truth but hiding something, or are they mostly lying?"

May 2002 responses: 21% said "telling the truth", 65% said they are "mostly telling the truth but hiding something", 8% said they are "mostly lying", 6% not sure. 3/30–4/1/04 CBS 24% said "telling the truth", 58% said they are "mostly telling the truth but hiding something", 14% said they are "mostly lying", 4% not sure. 4/8/04 CBS 21% said "telling the truth", 66% said they are "mostly telling the truth but hiding something", 10% said they are "mostly lying", 4% not sure. 4/23–27/04 24% said "telling the truth", 56% said they are "mostly telling the truth but hiding something", 16% said they are "mostly lying", 4% not sure. Oct 2006 responses: 16% said "telling the truth", 53% said they are "mostly telling the truth but hiding something", 28% said they are "mostly lying", 3% not sure.

CBS News and The New York Times have conducted a number of polls on the Iraq War that have included the question:

"Was Saddam personally involved in 9/11?" Poll conducted between September 4–8, 2007.

April 2003 responses: 53% said Yes, 38% said No. October 2005 responses: 33% said Yes, 55% said No. September 2006 responses: 31% said Yes, 57% said No. September 2007 responses: 33% said Yes, 58% said No.

Scripps Howard polls A poll from July 2006, sponsored by Scripps Howard and conducted by Ohio University, surveyed 1,010 randomly selected citizens of the United States, with a margin of error of 4 percent. The survey found that 36 percent thought it somewhat or very likely that U.S. officials either participated in the attacks or took no action to stop them because they wanted the United States to go to war in the Middle East. It made some statements relating to some of the 9/11 conspiracy theories and asked respondents to say whether they thought that the statements were likely to be true.

Federal officials either assisted in the 9/11 attacks or took no action to prevent them because they wanted the United States to go to war in the Middle East. 59% "not likely" 20% "somewhat likely" 16% "very likely" Part of survey "SHOH33," completed on July 6, 2006.

The collapse of the twin towers in New York was aided by explosives secretly planted in the two buildings. 77% "unlikely" 10% "somewhat likely" 6% "very likely" Part of survey "SHOH33," completed on July 6, 2006.

The Pentagon was struck by a military cruise missile in 2001 rather than by an airliner captured by terrorists. 80% "not likely" 6% "somewhat likely" 6% "very likely" Part of survey "SHOH33," completed on July 6, 2006.

In November 2007, Scripps Howard surveyed 811 Americans about their beliefs in several conspiracy theories and asked this question: How about that some people in the federal government had specific warnings of the 9/11 attacks in New York and Washington, but chose to ignore those warnings. Is this very likely, somewhat likely or unlikely? 32% "Very Likely" 30% "Somewhat Likely" 30% "Unlikely" 8% "Don't Know/Other"

Other United States polls

Rasmussen Reports published the results of their poll May 4, 2007. According to their press release, "Overall, 22% of all voters believe the President knew about the attacks in advance. A slightly larger number, 29%, believe the CIA knew about the attacks in advance. White Americans are less likely than others to believe that either the President or the CIA knew about the attacks in advance. Young Americans are more likely than their elders to believe the President or the CIA knew about the attacks in advance.", "Thirty-five percent (35%) of Democrats believe he did know, 39% say he did not know, and 26% are not sure." and "Republicans reject that view and, by a 7-to-1 margin, say the President did not know in advance about the attacks. Among those not affiliated with either major party, 18% believe the President knew and 57% take the opposite view."

A poll reported in The Washington Post in September 2003 found that nearly 70 percent of respondents believed Saddam Hussein was probably personally involved in the attacks.