Waterboarding is a form of torture that consists of immobilizing the victim on his or her back with the head inclined downwards, and then pouring water over the face and into the breathing passages. By forced suffocation and inhalation of water, the subject experiences drowning and is caused to believe they are about to die. It is considered a form of torture by legal experts, politicians, war veterans, medical experts in the treatment of torture victims, intelligence officials, military judges, and human rights organizations. As early as the Spanish Inquisition it was used for interrogation purposes, to punish and intimidate, and to force confessions.

In contrast to submerging the head face-forward in water, waterboarding precipitates an almost immediate gag reflex. The technique does not inevitably cause lasting physical damage. It can cause extreme pain, dry drowning, damage to lungs, brain damage from oxygen deprivation, other physical injuries including broken bones due to struggling against restraints, lasting psychological damage or, if uninterrupted, death. Adverse physical consequences can start manifesting months after the event; psychological effects can last for years.

In 2007 it was reported that the Central Intelligence Agency (CIA) was using waterboarding on extrajudicial prisoners and that the United States Department of Justice had authorized the procedure, a revelation that sparked a worldwide political scandal. Al-Qaeda suspects upon whom the CIA is known to have used waterboarding are Khalid Sheikh Mohammed, Abu Zubaydah, and Abd al-Rahim al-Nashiri.