In Philosophy of Law, Andrei Marmor provides a comprehensive analysis of contemporary debates about the fundamental nature of law--an issue that has been at the heart of legal philosophy for centuries. What the law is seems to be a matter of fact, but this fact has normative significance: it tells people what they ought to do. Is the normative content of a law entirely determined by the facts that make it a law? Are there some normative moral constraints on what the law can be? And can we fully characterize and define the law without assuming a moral conception about what the law ought to be?