 Legal positivism has a long history and a broad influence. It has antecedents in ancient political philosophy and is discussed, and the term itself introduced, in mediaeval legal and political thought (see Finnis 1996). The modern doctrine, however, owes little to these forbears. Its most important roots lie in the political philosophies of Hobbes and Hume, and its first full elaboration is due to Jeremy Bentham (1748–1832) whose account Austin adopted, modified, and popularized. For much of the next century an amalgam of their views, according to which law is the command of a sovereign backed by force, dominated English philosophical reflection about law. By the mid-twentieth century, however, this account had lost its influence among working legal philosophers. Its emphasis on legislative institutions was replaced by a focus on law-applying institutions such as courts, and its insistence of the role of coercive force gave way to theories emphasizing the systematic and normative character of law. The most important architects of contemporary legal positivism are the Austrian jurist Hans Kelsen (1881–1973) and the two dominating figures in the analytic philosophy of law, H.L.A. Hart (1907–92) and Joseph Raz, among whom there are clear lines of influence, but also important contrasts. Legal positivism’s importance, however, is not confined to the philosophy of law. It can be seen throughout social theory, particularly in the works of Marx, Weber, and Durkheim, and also among many lawyers, including the American “legal realists” and most contemporary feminist scholars. Although they disagree on many other points, these writers all acknowledge that law is essentially a matter of social fact. Some of them are, it is true, uncomfortable with the label “legal positivism” and therefore hope to escape it. Their discomfort is sometimes the product of confusion. Lawyers often use “positivist” abusively, to condemn a formalistic doctrine according to which law is always clear and, however pointless or wrong, is to be rigorously applied by officials and obeyed by subjects. It is doubtful that anyone ever held this view, but it is in any case false and has nothing to do with legal positivism. Among the philosophically literate another, more intelligible, misunderstanding may interfere. Legal positivism is here sometimes associated with the homonymic but independent doctrines of logical positivism (the meaning of a sentence is its mode of verification) or sociological positivism (social phenomena can be studied only through the methods of natural science). While there are historical connections and commonalities of temper among these ideas, they are essentially different. The view that the existence and content of law depends ultimately on social facts does not rest on a particular semantic thesis, and it is compatible with a range of theories about how one investigates the social world, including non-naturalistic accounts. To say that the existence of law depends on facts and not on its merits is a thesis about the relation among laws, facts, and merits, and not otherwise a thesis about the individual relata. Hence, many traditional “natural law” moral doctrines—including the belief in a universal, objective morality grounded in human nature—do not contradict legal positivism. The only influential positivist moral theories are the views that moral norms are valid only if they have a source in divine commands or in social conventions. Such theists and relativists apply to morality the constraints that legal positivists think hold for law.