Of all deception detection tools, the polygraph has the longest tradition. Still, the use of the polygraph for the detection of deception has been debated in the scientific literature for almost as long as it exists. This chapter highlights the promises and perils of the use of the polygraph for the detection of deception. It first critically discusses the rationale, accuracy and application of the widely used control question polygraph test, including its increased use in sex offender management. It then describes the current status, challenges and potential applications of a different testing format used in conjunction with the polygraph, namely, the concealed information test (CIT). Finally, the chapter highlights recent research on a potential new application of the CIT, namely, to extract information that is unknown to the investigative authorities, from either individuals or groups of suspects.