For as long as human beings have deceived each other, people have tried to develop techniques for detecting deception and determining truth. These techniques have almost always included interviews and interrogations to try to see through deception and reveal what a deceiver will not freely admit. In the 20th century, lie detection took on scientific aspects with the development of techniques that use measures of physiological responses as indicators of deception.

The best known of these is the polygraph. This technique, which relies on physiological measurements developed early in the century, has become for many in the U.S. law enforcement and intelligence communities (including counterintelligence officials in several agencies with whom we met) the most valued method for identifying criminals, spies, and saboteurs when direct evidence is lacking.

Polygraph examinations are widely used in the United States and in some other countries (notably, Israel, Japan, and Canada) for three main purposes: They are used for pre employment screening in law enforcement and pre employment or pre clearance screening in agencies involved in national security, they are used for screening current employees, especially in security-sensitive occupations and they are used in investigations of specific events, for instance, in criminal cases.