legal concept is that of "fitness to plead". As an expert witness Forensic psychiatrists are often called to be expert witnesses in both criminal and civil proceedings. Expert witnesses give their opinions about a specific issue. Often, the psychiatrist will have prepared a detailed report before testifying. The primary duty of the expert witness is to provide an independent opinion to the court. An expert is allowed to testify in court with respect to matters of opinion only when the matters in question are not ordinarily understandable to the finders of fact, be they judge or jury. As such, prominent leaders in the field of forensic psychiatry, from Thomas Gutheil to Robert Simon and Liza Gold and others have identified teaching as a critical dimension in the role of expert witness. The expert will be asked to form an opinion and to testify about that opinion, but in so doing will explain the basis for that opinion, which will include important concepts, approaches, and methods used in psychiatry. Mental state opinion Mental state opinion (MSO) gives the court an opinion, and only an opinion, as to whether a defendant was able to understand what he/she was doing at the time of the crime. This is worded differently in many states, and has been rejected altogether in some, but in every setting, the intent to do a criminal act and the understanding of the criminal nature of the act bear on the final disposition of the case. Much of forensic psychiatry is guided by significant court rulings or laws that bear on this area which include these three standards: M'Naghten rules: Excuses a defendant who, by virtue of a defect of reason or disease of the mind, does not know the nature and quality of the act, or, if he or she does, does not know that the act is indeed wrong. Durham rule: Excuses a defendant whose conduct is the product of mental disorder. ALI test: Excuses a defendant who, because of a mental disease or defect, lacks substantial capacity to appreciate the criminality (wrongfulness) of his or her conduct or to conform his conduct to the requirements of law. "Not guilty by reason of insanity" (NGRI) is one potential outcome in this type of trial. Importantly, insanity is a legal and not a medical term. Often, psychiatrists may be testifying for both the defense and the prosecution. Forensic psychiatrists