Since the March 2003, U.S.-led invasion of Iraq, rumors have persisted of a United States plan to attack Iran. Some U.S. officials are apparently willing to contemplate the use of military force to prevent Iran from developing nuclear weapons. Under international law, however, there is no right without Security Council authorization to use significant military force on the territory of another state to stop nuclear research. Knowing this, alternative arguments are being floated by those sympathetic to the plan to attack Iran. One such argument asserts that the U.S. could attack Iran on the basis of collective self-defense with Iraq or Israel. This article makes clear that the United States in fact has no right to attack Iran on the basis of...