Few outside countries have more at stake in the evolution of Iran’s political situation than the United States, which has been in a state of open enmity with the Islamic Republic for more than three decades. Threats of Iran-backed terrorism, Tehran’s apparent nuclear ambitions, and its evident aim of destabilizing American allies—chiefly Israel—are perpetually high on the list of US concerns in the region. Why is Iran so important to the US? What explains the enduring animosity between the two countries? Answers to these and other questions about the United States’ position in the region today can be found by looking back to the Cold War.