Although thousands of polygraph tests are performed each year, detection of deception using the polygraph ("lie detector") remains controversial. Polygraph tests need to meet the same criteria as other psychological tests in order to be regarded scientific. Most importantly, polygraph tests need to be accurate and have a good theory (National Research Council, 2003). The Concealed Information Test is a polygraph test with good accuracy and a well developed theory. The idea behind the test is simple and elegant. The perpetrator of a crime knows things about the crime, of which an innocent is unaware. When confronted with this crime information, only the guilty will recognize it and is likely to show a bodily response towards it. Still, the theory of the Concealed Information Test needs further empirical verification. This book describes a series of studies on the theory of the Concealed Information Test. The data generally support the theory of the Concealed Information Test. These findings suggest that the Concealed Information Test can be a useful forensic tool for criminal investigations.