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 collective self-defense either. International law prohibits the use of force except in response to an armed attack that is occurring or with Security Council authorization. Even when one of these two exceptions to the general prohibition exists, any lawful use of force must have a chance of succeeding - of accomplishing the military objective. Moreover, and most importantly in the case of Iran, any use of force must have a chance of succeeding in a way that does not cause disproportionate death, injury, or destruction. Iran's nuclear research sites are buried deep in the ground and scattered throughout the country near major population centers. Bombing these sites will accomplish little beside the deaths of many innocent people. The article concludes that the great legal and moral imperative to preserve the peace mandates that the United States find means other than military force to respond to Iran's nuclear ambitions. Negotiation has succeeded in the past in persuading states to give up nuclear weapons and nuclear weapon programs. Renewed United States commitment to negotiation, to the peaceful settlement of disputes and to international law in general will give it new authority to demand that Iran and all states respect their own international law obligations, including the obligation not to acquire nuclear weapons. Iran, nuclear weapons, Nuclear Non-Proliferation Treaty, self-defense, collective self-defense, United Nations, United Nations Charter, United Nations Security Council, necessity and proportionality, international law, Nicaragua Case, Bosnia v. Serbia, Oil Platforms, state responsibility