How does the law regard and define mental incompetence? To what extent has the law relied on extra-legal authorities - be they religious or scientific - to frame its own categories of mental incompetence? This text takes readers on a journey through the changing historical landscape of human nature and offers a look at the legal conceptions of insanity from the pre-classical Greek world to the present. It should be of use to those interested in the evolution of thinking about legal insanity.