Legal positivism is a school of thought of philosophy of law and jurisprudence, largely developed by nineteenth-century legal thinkers such as Jeremy Bentham and John Austin. However, the most prominent figure in the history of legal positivism is H.L.A. Hart, whose work The Concept of Law caused a fundamental re-thinking of the positivist doctrine and its relationship with the other principal theories of law. In more recent years the central claims of legal positivism have come under significant attack from Ronald Dworkin.

It is difficult to summarize positivist thinking, but it is generally accepted that the central claim of legal positivism is the following:

"In any legal system, whether a given norm is legally valid, and hence whether it forms part of the law of that system, depends on its sources, not its merits."

Legal positivists make some distinctive claims about what constitutes legal validity. It is difficult to improve on the following introduction offered by Leslie Green: "Whether a society has a legal system depends on the presence of certain structures of governance, not on the extent to which it satisfies ideals of justice, democracy, or the rule of law. What laws are in force in that system depends on what social standards its officials recognize as authoritative; for example, legislative enactments, judicial decisions, or social customs. The fact that a policy would be just, wise, efficient, or prudent is never sufficient reason for thinking that it is actually the law, and the fact that it is unjust, unwise, inefficient or imprudent is never sufficient reason for doubting it. According to positivism, law is a matter of what has been posited (ordered, decided, practiced, tolerated, etc.); as we might say in a more modern idiom, positivism is the view that law is a social construction."