Can customary international law be used in U.S. courts? The question was recently before the Supreme Court in Turkiye Halk Bankasi A.S. v. United States. This Essay argues that adopting precedential status for CIL would provide clarity for litigants and lower courts, maintain flexibility for the political branches, and fulfill the constitutional role of an active judiciary in foreign affairs. By examining Supreme Court decisions, the history of the Constitution’s drafting, and past practice, this Essay provides a framework for understanding how CIL can be applied domestically.