It has been twenty years since the US Court of Appeals for the Second Circuit issued its landmark decision in Filartiga v Pena-Irala.1 In upholding federal court jurisdiction over a suit between aliens concerning violations of international human rights standards in a foreign country, the court in Filartiga paved the way for modern international human rights litigation. As Professor David Bederman has observed, [iln a sense, all current human rights litigation owes its fortune to Filartiga.2 Since Filartiga, US courts have been confronted with two waves of international human rights litigation. The first has primarily involved suits, like Filartiga itself, between aliens concerning alleged human rights abuses occurring outside the United States. This has been moderately successful. While enforcement of judgments is often a problem in these cases, many courts have at least been receptive to hearing the plaintiffs' claims. In recent years, litigants have increasingly attempted to apply the principles developed in this first litigation to suits against domestic defendants. This second wave litigation has been much less successful than the first wave. More importantly, the failure of this litigation-especially in cases involving US plaintiffs-- has the potential to unravel some of the successes achieved in the first wave. To understand this point, some background is necessary. There are two principal types of international law-treaties and customary international law. International human rights litigation has not primarily involved treaty claims. There are of course many treaties today that govern human rights, but the United States either has not ratified these treaties, or it has declared them to be non-self-executing-that is, not enforceable in US courts until implemented by Congress. Consequently, international human rights litigation in the United States is primarily based on claims under customary international law-the that results from a general and consistent practice of states followed by them from a sense of legal obligation.3 The text of the Constitution says little about the domestic status of customary international law. It says a number of things about the status of treaties-in particular, it tells us that they are of the supreme of the land and that federal courts may hear cases arising under them.4 The only reference in the Constitution to customary international law, however, is a grant of statutory power to Congress to define and punish offenses against customary international (referred to at the time of the founding as of the of nations).5 In several decisions in the 19th and early 20th centuries, the Supreme Court referred to the of nations as part of our law or part of the of the land.6 In practice, courts treated customary international as general common law-a background source of for federal and state courts in the absence of any federal or state legislation to the contrary. Federal court interpretations of this general common were not binding on the state courts, and claims arising under this general common did not fall within the federal question jurisdiction of the federal courts.7 In Erie Railroad v Tompkins,8 the Supreme Court held that federal courts were no longer free to apply general common law-the choice was either federal or state law.9 On the same day it decided Erie, however, the Court held that for some issues it is appropriate for federal courts to create federal common law-common that is truly federal in that it is binding on the states and provides a basis for federal question jurisdiction.10 The Supreme Court has not had occasion since Erie to resolve the status of customary international law. There is dicta in the Supreme Court's Sabbatino decision11 that could be read as endorsing a federal common status for customary international law,12 but that was not the holding of the Court; indeed, the Court in Sabbatino refused to apply in that case customary international governing expropriation of foreign citizen property. …