Abstract: Originalism, best understood, is not a theory of interpretation but a theory of our law. Its central claim is that the Founders' law remains good law for us today. And it ought to be defended, if at all, based not on normative goals or abstract philosophy, but on positive features of American legal practice and of our rules for legal change. A basic assumption of legal systems is that the law, whatever it is, stays the same until it's lawfully changed. Originalism begins this process with an origin, a Founding. Whatever rules we had when the Constitution was adopted, we still have today -- unless something legally relevant happened along the way to change them. We expect assertions of constitutional change to provide this kind of historical pedigree; and a wide variety of approaches -- "conservative" and "liberal," from precedent to post-Founding practice -- are defended as products of the Founders' law. These ordinary practices show an implicit commitment to a deeply originalist premise: that our law today consists of their law, the Founders' law, plus any lawful changes. What’s important about the Constitution, on this account, isn't so much what its text said, but what its enactment did -- what it contributed to American law at the Founding, as preserved to the present day. Rather than look to original intentions, original public meaning, and so on, we should look to the original law -- the law added to our system by the text's enactment, according to the legal rules governing interpretation at the time. This "original-law originalism" helps us to understand, and hopefully to resolve, longstanding constitutional debates: originalists and nonoriginalists ought to disagree about the sources of today's law, while different schools of originalists ought to disagree about the law's content in the past. The claim that we still take as our own the Founders' law, as it's been lawfully changed, is a claim about current society; it might be true or false. This Article merely argues that, if it is true, it's the best reason to be an originalist -- and, if it's false, the best reason not to.