With current concerns over security, it is becoming increasingly important to discriminate between suspects who lie versus those who tell the truth. Nevertheless, a substantial empirical base shows that laypeople and even trained investigators (e.g., police) are often poor at discriminating between truth tellers and liars (Vrij, 2004(Vrij, , 2008. Vrij (2008) reviewed 107 lie detection studies (79 studies with laypeople and 28 studies with trained investigators) in which observers attempted to detect truths and lies told by people they did not know. The observers did not have any factual evidence to rely on and had to base their judgments solely on the nonverbal and verbal behavior displayed by the truth tellers and liars. The accuracy rates obtained by laypeople (54.27%) and trained investigators (55.91%) were similar and only just above the accuracy rate that could be expected by merely tossing a coin (50%). (O' Sullivan & Ekman, 2004, and O'Sullivan, 2005, 2007, claim to have discovered 29 individuals with superior lie detection skills after having tested over 12,000 professionals for their expertise in lie detection. They call them "wizards." See Bond & Uysal, 2007, for a statistical critique of the evidence for this claim.)One important difficulty observers face is that the act of lying per se does not result in any nonverbal or speech-related cues to deceit (DePaulo et al., 2003;Vrij, 2008). In other words, reliable cues to deception, akin to Pinocchio's growing nose, do not exist; therefore, there is no cue that the lie detector can truly rely on. In this light, the Screening Passengers by Observation Technique introduced at airports in the United States and soon to be introduced in United Kingdom airports can be seen as limited. Screening Passengers by Observation Technique teams look for signs of erratic behavior among passengers and thus assume that the mere fact of hiding something, or other forms of lying, result in unique patterns of behavior displayed by passengers. (This is based largely on the work of Paul Ekman, who claims that aspects of facial communication are beyond control and can betray a deceiver's true emotion via micro-expressions [lasting 1/25 to 1/5 of a second] of that emotion; Ekman, 2006; Porter & Ten 97 The project described in this chapter was sponsored by grants from the Economic and Social Research Council (RES-000-23-0292 and RES-000-22-1632).