The insanity excuse has been around for a long time, even as society’s social and scientific understandings of insanity have evolved. As an excuse, rather than a justification, insanity doctrine does not hold that the criminal act was morally correct, but rather that the insane person is not responsible for a morally wrong action. The cases and readings in this section introduce some of the formulations of the insanity defense that are currently in use. Consider how the various formulations balance the moral and the medical. According to one insanity rule, the ability to tell right from wrong is central to the insanity inquiry. According to another, self-control is key, as an irresistible impulse may excuse culpability. The Model Penal Code applies a sort of hybrid. Each major test is followed in a variety of jurisdictions, and some jurisdictions follow yet another test or provide for no insanity defense at all. What does the sheer diversity of approaches and standards tell us about the insanity excuse? Should the very diversity of approaches implicate fairness concerns? Consider why our criminal justice system may not seek to punish the insane. How does insanity implicate the traditional justifications of punishment (retribution, deterrence, incapacitation, and rehabilitation)? Since criminal punishment undoubtedly has a moral component, what should be the role of science in defining who is insane and who is excused due to insanity? Are those the same questions, or are they different? Lastly, insanity may implicate more than the question of excuse. Even if someone is guilty, they may be “guilty but mentally ill.” Consider what role insanity or mental illness may play in establishing the other elements of a crime, such as mens rea.