Waterboarding is an interrogation technique illegal in the United States but used by the CIA under the Bush administration. A presidential finding, signed in 2002, by President Bush, Condoleezza Rice and then-Attorney General John Ashcroft approved various torture techniques, including waterboarding.
The objective of waterboarding is to mentally traumatise the victim by making them believe that they are just about to die. The victim is strapped upside down to a board that is at an angle in order to enhance their disorientation and keep the head at the right angle for the experience of drowning. The victim has cellophane or a cloth wrapped around the head so that they can't see. A small opening is left for the mouth, and water is poured over their head and into this opening in order to induce the feeling of drowning. Within a few seconds of this experience the victim usually 'cracks' and divulges whatever information their torturer is asking about regardless of its authenticity (interrogation under torture is very unreliable). Waterboarding torture can result in a variety of injuries to the victim both physically and mentally. Physical results can be broken limbs due to struggling against the restraints, damage to lungs due to breathing in the water, and death (its not uncommon for the faked drowning to actually become real by mistake). The mental trauma of this torture is significant, and will often include post traumatic stress disorder. Waterboarding was first used by the Italian inquisition in the 1500s.
Thankfully president Obama recently banned US special forces from using waterboarding as well as ordering that the US special forces 'black sites' (used for torture) around the world to be shut down, but he stated that he did not think that those who used the technique under the bush administration should face trial. International law dictates that those responsible for torture should face trial, US special forces should not be above the law.

Gulf War veteran Joe Tougas, dressed as a Guantanamo Bay detainee, volunteered to be waterboarded during a demonstration at UC Berkeley to show that the practice is a severe form of torture. – Photo: John Han