Although international law has figured prominently in many disputes around actions of the U.S. military, the precise relationship between international law and the President's war powers has gone largely unexplored. This Article seeks to clarify one important aspect of that relationship: the role of international law in determining the scope of Congress's general authorizations for the use of force. In the seminal case of Hamdi v. Rumsfeld, the plurality opinion used international law to interpret the authorization by Congress for the use of force, but did so without adequate attention to the content or interpretive function of international law. This Article identifies and defends a better approach: courts should presume that general authorizations for the use of force do not empower the President to violate international law. Such a presumption is consistent with long-standing tools of statutory interpretation reflected in the Charming Betsy canon, maximizes the presumed preferences of Congress, advances separation of powers values, and promotes normative values that favor the use of international law as an interpretive tool.