 The present topic, the question of the limits of law, is widely understood to be one of the important evaluative questions, revolving around the legal enforcement of morality. In the nineteenth century John Stuart Mill proposed “the harm principle” as his answer; in the late twentieth century H.L.A Hart adopted a significantly modified version of Mill’s principle and further important versions of the harm principle followed in the hands of Joel Feinberg and Joseph Raz (Sections 4–6 below). The harm principle in all its manifestations has encountered strong resistance, most notably from “legal moralists” (Sections 1–3) and remains in the eyes of many the focus of debate, the view to adopt, supplement or modify (as some would say), or to beat and replace (as others would say).