"Enhanced interrogation techniques" or "enhanced interrogation" was a program of systematic torture of detainees by the Central Intelligence Agency (CIA), the Defense Intelligence Agency (DIA) and various components of the U.S. Armed Forces at remote sites around the world — including Abu Ghraib, Bagram, Guantanamo Bay, Rabat, Udon Thani, Vilnius, Bucharest and Stare Kiejkuty — authorized by officials of the George W. Bush administration. Methods used included beating, binding in contorted stress positions, hooding, subjection to deafening noise, sleep disruption, sleep deprivation to the point of hallucination, deprivation of food, drink, and medical care for wounds, as well as waterboarding, walling, sexual humiliation, rape, sexual assault, subjection to extreme heat or extreme cold, and confinement in small coffin-like boxes. A Guantanamo inmate's drawings of some of these tortures, to which he himself was subjected, were published in The New York Times. Some of these techniques fall under the category known as "white room torture". Several detainees endured medically unnecessary "rectal rehydration", "rectal fluid resuscitation", and "rectal feeding". In addition to brutalizing detainees, there were threats to their families such as threats to harm children, and threats to sexually abuse or to cut the throat of detainees' mothers.

The number of detainees subjected to these methods has never been authoritatively established, nor how many died as a result of the interrogation regime, though this number could be as high as 100. The CIA admits to waterboarding three people implicated in the September 11 attacks: Abu Zubaydah, Khalid Sheikh Mohammed, and Mohammed al-Qahtani. A Senate Intelligence Committee found photos of a waterboard surrounded by buckets of water at the Salt Pit prison, where the CIA had claimed that waterboarding was never used. Former guards and inmates at Guantánamo have said that deaths which the US military called suicides at the time, were in fact homicides under torture. No murder charges have been brought for these or for acknowledged torture-related homicides at Abu Ghraib and at Bagram.

From the outset, there were concerns and allegations expressed that "enhanced interrogation" violated U.S. anti-torture statutes or international laws such as the UN Convention against Torture. In 2005, the CIA destroyed videotapes depicting prisoners being interrogated under torture; an internal justification was that what they showed was so horrific they would be "devastating to the CIA", and that "the heat from destroying [the videotapes] is nothing compared to what it would be if the tapes ever got into public domain". The United Nations special rapporteur on torture, Juan Mendez, stated that waterboarding is torture—"immoral and illegal", and in 2008, fifty-six Democratic Party members of the US Congress asked for an independent investigation.

American and European officials including former CIA director Leon Panetta, former CIA officers, a Guantanamo prosecutor, and a military tribunal judge, have called "enhanced interrogation" a euphemism for torture. In 2009, both President Barack Obama and Attorney General Eric Holder said that certain techniques amount to torture, and repudiated their use. They declined to prosecute CIA, US Department of Defense, or Bush administration officials who authorized the program, while leaving open the possibility of convening an investigatory "Truth Commission" for what President Obama called a "further accounting".

In July 2014, the European Court of Human Rights formally ruled that "enhanced interrogation" was tantamount to torture, and ordered Poland to pay restitution to men tortured at a CIA black site there. In December 2014, the U.S. Senate published around 10% of the Senate Intelligence Committee report on CIA torture, a report about the CIA's use of torture during the George W. Bush administration.

Almost immediately after the 9/11 attacks, Bush administration officials conferring by video link from bunkers decided to treat the attacks as acts of war, rather than crimes. The question arose: were captured prisoners to be treated as prisoners of war? Officials including Justice Department lawyer John Yoo recommended classifying them as "detainees" outside the protection of the Geneva Conventions or any other domestic or military law, and incarcerating them in special prisons instead of the barracks-like "prisoner-of-war camp you saw in Hogan's Heroes or Stalag 17." On September 17, 2001, President Bush signed a still-classified directive giving the CIA the power to secretly imprison and interrogate detainees.

In late 2001, the first detainees including men like Murat Kurnaz and Lakhdar Boumediene, later established to be innocent and arrested on flawed intelligence or sold to the CIA for bounties, were brought to hastily improvised CIA/military bases such as Kandahar, Afghanistan. They were subjected to beatings, electric shocks, exposure to extreme cold, suspension from the ceiling by their arms, and drowning in buckets of water. An unknown number died as a result. In late 2001 and early 2002, interrogation under torture at secret sites was still ad hoc, not yet organized as a bureaucratic program, nor sanctioned under US Justice Department legal cover.

As early as November 2001, the CIA general counsel began considering the legality of torture, writing that "the Israeli example" (using physical force against hundreds of detainees) could serve as "a possible basis for arguing ... torture was necessary to prevent imminent, significant, physical harm to persons, where there is no other available means to prevent the harm."