The defense of insanity is codified in s. 16 of the Canadian Criminal Code, and these provisions are derived from the M'Naghten Rules, while containing an important modification. The code states that no person shall be convicted of an offense while he is 'insane,' and legal insanity is considered to exist when a person is in a state of natural imbecility or has a 'disease of the mind' that renders him incapable of appreciating the nature and quality of an act or of knowing that it is wrong. Normally, when a defense of insanity is raised, there is general agreement that the accused has some medically recognized mental disorder. The crucial legal question is whether the mental disorder rendered the accused incapable of appreciating the nature and quality of the act or of knowing that it was wrong. The term 'wrong' has been variously interpreted as legally or morally wrong. It is generally agreed that a person may know that an act is against the law but may still be incapable of appreciating the nature and quality of the act. If a person is capable of appreciating the nature and quality of the act and of knowing that it is wrong, then he is not inculpable merely because he was unable to restrain his impulse to do the act. Automatism is the term used to denote unconscious involuntary behavior; it may be produced by disease of the mind or by some external cause, such as a blow on the head or drugs. Automatism due to disease of the mind is subsumed under the defense of insanity and is described as insane automatism. The insanity defense is deeply rooted in the legal system, based on the concept of criminal intent and fault, and should continue to evolve under further judicial and legislative influences. Forty-three notes are provided.