Iran's nuclear program remains one of the most contentious issues of modern international politics. This book is the first to trace the evolution of Iran's nuclear strategy (program) in the broader context of its relationship with the United States, from the early days of total US support in the 1950s to the staunch opposition that followed the Iranian revolution, and its reconstitution. The account covers the pivotal moments including initial meetings to pursue uranium enrichment in Iran, key internal debates, the signing of the Joint Comprehensive Plan of Action (JCPOA), Donald Trump's controversial withdrawal and the latest efforts to revive the agreement. The book shows that because the strategic logic of the nuclear program transcends the regimes type, dismantling the Iranian nuclear program is not viable policy option for the United States. Instead, the US must learn to live with a nuclear threshold state and make it a priority to keep Iranian capacity as far away from the bomb as possible. The research is based on American declassified documents and often marginalized Iranian primary sources including political memoirs, diplomatic correspondences, oral histories from Iranian nuclear officials and exclusive one-on-one interviews with Iranian scientists and national security officials. The account and its findings have important implications for both scholars of nuclear non-proliferation and for policymakers.