This paper seeks to provide a sociological account of one aspect of a highly significant redefinition of the moral boundaries of English society: a redefinition which saw the transformation of insanity from a vague, culturally defined phenomenon afflicting an unknown, but probably small, portion of the total population into a condition which could only be authoritatively diagnosed, certified, and dealt with by a group of legally recognized experts and which was now seen as one of the major forms of deviance in English society. Where in the eighteenth century only the most violent and destructive amongst those now labelled insane would have been segregated and confined apart from the rest of the community, by the mid-nineteenth century, with the achievement of lunacy ‘reform’, the asylum was endorsed as the sole officially approved response to the problems posed by all forms of mental illness. In what follows, I want to focus attention rather closely on one centrally important feature of this whole process—and that is just how that segment of the medical profession which we now call psychiatry captured control over insanity; or, to put it another way, how those known in the early nineteenth century as mad-doctors first acquired a monopolistic power to define and treat lunatics. I shall begin, though, with some general remarks on the sociological importance of the issues I shall be raising here.