In preparing the State's case, prosecutors should conduct a thorough investigation of all potential witnesses and advise all officers who have contact with potential insanity defendants to record even their most trivial observations. As soon as the likelihood of the insanity issue arises, prosecutors should develop a strategy focusing on three areas: the facts of the particular case, the mental responsibility laws of the jurisdiction, and the method of trial--by court or by jury. At the beginning of the trial, prosecutors should seek to establish a good relationship with the jury and to inform the jurors about the legal implications of the insanity defense. Prosecutorial tactics in the course of the trial include attacking the psychiatrist's education, experience, or subject knowledge, pointing out the weaknesses of particular psychological tests, and impeaching the expert. Techniques for cross-examining the defendant are summarized, though this opportunity seldom arises with insanity cases. One crucial phase in the prosecution's attack is the selection, preparation, and testimony of the State's expert witness. In their closing arguments, prosecutors should point out to court and jury that there is a legal test of insanity: defendants must have a mental disease or defect as a result of which they are unable to appreciate the criminality of their acts or to conform their conduct to the requirements of law. The guide includes numerous appendixes including a case digest, sample forms regarding mental disease or defect and a selected bibliogaphy.