Abstract: Many scholars believe that customary international law (CIL) has the status of self-executing federal common law, to be applied by courts in the United States without any need for it to be enacted or implemented by Congress. In an article last year, we argued that this view lacks historical support and is in substantial tension with political branch enactments as well as broader constitutional principles of separation of powers, federalism, and representative democracy. We concluded that CIL should not be treated as federal law in the absence of authorization from the federal political branches. In the May 1998 issue of the Harvard Law Review, Professor Harold Koh argues that our analysis and conclusion are "radical," "utterly mistaken," and "bizarre." In this response to Koh's article, we focus on the four central errors in Koh's analysis: (a) its mistaken use of history; (b) its conflation of the traditional CIL that regulates international relations with the new CIL of human rights that regulates the way a nation treats its citizens; (c) its unjustifiably broad conception of the common law powers of federal courts; and (d) its unwarranted assumption that all of international law must be incorporated into domestic law.