Mental health professionals assist Australian courts and tribunals with explanations about human behaviour and mental processes related to offending behaviour. Contrary to other witnesses who are only allowed to give evidence in relation to what they directly heard or saw, mental health professionals are allowed to express opinions because they are recognised as expert witnesses with specialised knowledge. However, in Australia at least, little is known about how these expert witnesses are chosen and how they meet the requirements of possessing “specialised knowledge”. In this article, we provide a brief history of expert witnesses in the courtroom, including the use of psychologists as expert witnesses. We then highlight some of the concerns that legal professionals have raised about psychologists as expert witnesses in the limited number of studies that have been conducted in Australia, the United States, and the United Kingdom. Finally, we raise questions about how psychologists are chosen to be expert witnesses in Australia and introduce directions for future research.