Abstract: Erie Railroad Co. v. Tompkins is the most important case that no one who isn’t a lawyer has ever heard of. Viewed narrowly, it holds that a federal court, when deciding issues subject to state law, has to defer to the opinions of state courts. That proposition is often false. But the problem with Erie isn’t this narrow result; the problem is its reasoning. As the Supreme Court would later put it, Erie overruled, not just a past line of cases, but “a particular way of looking at law.” Erie rejected a category of law—sometimes called general common law, or just “general law”—which was fundamental to our federal system, and the absence of which has left us unable to understand basic aspects of American jurisprudence. This lecture, delivered on the occasion of the author’s appointment as Antonin Scalia Professor of Law, explores what life will look like after Erie—how the law will operate on the happy and glorious day when Erie has been overturned. This is not a prediction that Erie will be overturned. Though some legal seismologists have discerned rumblings in that direction, we have no guarantee that courts will get things right: the arc of jurisprudence does not always bend toward intellectual coherence. Rather than make predictions, it sets out a research agenda, attempting to think through some of the problems overruling Erie may pose—so that when the time comes to reconsider Erie, those who do so will have a clear path to follow. The most important feature of life after Erie may not be any particular doctrines the courts enforce, but the attitude with which they enforce them. To reject Erie is to recognize, as Francis Bacon put it, and as Justice Scalia noted in Rogers v. Tennessee, that the judge’s “office is jus dicere, and not jus dare; to interpret law, and not to make law, or give law.” When this power to make law is conferred by a statute or a constitution, maybe a judge can lawfully wield it. But one hopes that, after Erie, we will recognize this authority as one that no officials, least of all judges, have any right to arrogate to themselves.