More than four decades have passed since the onset of the strategic confrontation between the Islamic Republic of Iran and the United States. Throughout this period governments in both Tehran and Washington have changed the international environment has undergone profound transformation the Soviet Union has collapsed the unipolar moment has emerged and gradually given way to signs of an increasingly multipolar order. Yet despite these sweeping changes one of the most enduring features of contemporary international politics has remained the persistence of tensions between Iran and the United States.