The 1980–88 Iran-Iraq War stands as the pivotal event for Iran's national security strategy, especially as it pertains to the country's controversial nuclear program. The “imposed war,” as it is known to Iranians, caused Iran to view itself as isolated and on the defensive, striving for self-reliance and survival in what it continues to perceive as an unjust international order. The war has shaped both Iran's strategic outlook generally and its nuclear policies specifically. It was a decisive factor in determining the nature and scope of Iran's nuclear activities, as well as in Iran's approach to the international negotiations surrounding those activities, which in 2015 produced the Joint Comprehensive Plan of Action. Both during those talks and after the implementation of the deal began, Iranian decisionmakers regularly invoked the history and lessons of the war to construe their decisionmaking process and define their bottom lines. Yet the war and its implications for Iran's strategic culture and nuclear thinking remain understudied and misunderstood. If the implementation of the deal and a longer-term resolution of the conflict over Iran's nuclear program are to succeed, the history of the Iran-Iraq War and the vital lessons that Iran has drawn from it must be appreciated.