Ten years ago, the conventional wisdom among international law academics was that customary international law (CIL) had the status of self-executing federal common law to be applied by courts without any need for political branch authorization. This modern position came under attack by so-called revisionist critics who argued that CIL had the status of federal common law only in the relatively rare situations in which the Constitution or political branches authorized courts to treat it as such. Modern position proponents are now claiming that the Supreme Court\u27s 2004 decision in Sosa v. Alvarez-Machain confirms that CIL has the status of self-executing federal common law. As this Article explains, the decision in Sosa did not in fact embrace the modern position, and, indeed, is best read as rejecting it. Commentators who construe Sosa as embracing the modern position have confounded the automatic incorporation of CIL as domestic federal law in the absence of political branch authorization (i.e., the modern position) with the entirely different issue of whether and to what extent a particular statute, the Alien Tort Statute ( ATS ), authorizes courts to apply CIL as domestic federal law. The Article also explains how CIL continues to be relevant to domestic federal common law despite Sosa\u27s rejection of the modern position. The fundamental flaw of the modern position is that it ignores the justifications for, and limitations on, post-Erie federal common law. As the Article shows, however, there are a number of contexts in addition to the ATS in which it is appropriate for courts to develop federal common law by reference to CIL, including certain jurisdictional contexts not amenable to state regulation (namely admiralty and interstate disputes), and gap-filling and interpretation of foreign affairs statutes and treaties. The Article concludes by considering several areas of likely debate during the next decade concerning the domestic status of CIL: corporate aiding and abetting liability under the ATS; application of CIL to the war on terrorism; and the use of foreign and international materials in constitutional interpretation
