First published in 1999, The book examines the magnitude of the polemic surrounding each attempt to reformulate the insanity defence in the United States, England and Ireland. The book contains a critique of the McNaghten Rules, the defence of irresistible impulse, the product test of insanity, the justly responsible test, the American Law Institute’s test of insanity and the Butler Committee’s proposed revision. At the heart of the controversy surrounding each reformulation has been a medico-legal tension over the wording of the insanity defence and whether law or psychiatry’s view of insanity should prevail. The book looks at the success of the English diminished responsibility defence in abating the controversy. The result of introducing this defence has been the emergence of the legal and medical professions from a state of cold war to entente cordiale. The book explores the reasons for the diminished responsibility defence’s success in resolving the polemic over the insanity defence.