Deception poses a major threat to the accuracy of forensic evaluations and becomes more pervasive as the incentives get larger. In criminal and civil forensic settings, individuals may deliberately fabricate or exaggerate psychiatric or physical symptoms (i.e., malingering) in an effort to evade responsibility or sanctions for their actions, or to obtain some sort of other benefits (e.g., financial compensation). In other forensic contexts, individuals may intentionally minimize psychiatric symptoms or present themselves in an overly positive light (i.e., defensiveness) in order to maintain or reinstate privileges, such as release from a custodial setting. Both malingering and defensiveness are highly prevalent in forensic settings, although the frequency varies across contexts and successful feigners or minimizers may go undetected. As a result, psychologists are increasingly tasked with the role of evaluating the validity of an individual’s reported symptoms and clinical presentation. It is essential that psychologists be equipped with the knowledge and techniques to accurately detect deceptive behaviour in order to preserve the integrity of the legal process and protect those who are genuinely mentally ill from being wrongly identified as malingering. The aim of this chapter is to familiarize readers with malingering and defensiveness. Explanatory models and typologies of malingering are described, in addition to a review of prevalence rates for malingering and defensiveness in various forensic settings. Finally, we review common detection strategies for deceptive response styles, including those for exaggerated or minimized psychiatric symptoms, cognitive impairment, and psycho-legal abilities.