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Santa Clara Law Review

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The use of customary international law ("CIL") by courts in the United States, long the subject of debate among scholars, has finally come to the attention of the Supreme Court. In the last few years, the Court has interpreted and applied CIL to interpret provisions of the U.S. Constitution, to interpret statutes and treaties, and as a substantive rule of decision. While the Supreme Court's renewed interest in customary international law has drawn much praise, it has also sparked sharp criticism. The purpose of this symposium essay is not to recapitulate these disagreements, but instead, to identify a different problem with the interpretive and substantive use of CIL by federal and state courts. Whether a court uses CIL as a tool for statutory or constitutional interpretation or as a substantive rule of decision, the court's usage creates potentially serious structural conflicts in the U.S. constitutional system.