As polygraph and behavioural cues to deception have been discredited by scientists, the world of lie detection in law enforcement has become increasingly reliant on methods involving the analysis of language or metalanguage such as facial expressions. Several popular methods use a written statement from the subject and apply criteria to the text which are intended to separate statements based on actual events from statements based on the author’s imagination. However, the science surrounding these methods is equally damning, and that science is linguistics. This chapter demonstrates the important role for linguists, both in testing methods of language-based lie detection and in analysing the discourse that supports the use of such methods.