This chapter considers the ways in which the criminal law treats people suffering from mental disorders. The following controversies are examined: when an individual can be regarded as mentally incapable of being tried; the relationship between insane and sane automatism; the extent to which the insanity defence reflects modern psychiatric practice; whether the lack of direct correlation between the medical and legal definitions of ‘insanity’ infringes the European Convention on Human Rights (ECHR); and how the insanity defence ought to be reformed.