The spread of nuclear weapons is one of the greatest threats to world peace and has generateda scholarly debate concerning what underlying factors drive nuclear proliferation.Iran had for many years been accused of trying to develop a clandestine nuclear weapons programwhich has been a source of great concernon the world stage.The aim of thispaper is to understand Iran ́s decision to sign the JCPOA and thereby refraining from building nuclear weapons.Three non-proliferation models;the security model, the domestic model and the norms modelwill be used to analyze Iran ́s decision and to test theirrespectiveexplanatory power. The findings of this paper show thatseveral factors contributed to Iran ́s decision to sign the JCPOA. First, economic sanctionscontributed to a strong publicopposition to the regimes nuclear policies. Second, a negative image of the nuclear program in the eyes of the population further amplified public opposition.These two factors put pressure on the regime to find a solution to the nuclear issuebecause they saw this public opposition as a threat to their survival.Third, anincreased influence ofanti-nuclear factionsin Iran ́s political systemput increased pressure on the Supreme Leader to find a solution to the nuclear issue. Fourth, the regimes perception that a nuclear weapon would decreaseIran ́s security which reduced the incentives to proliferate. All these factors put together created the circumstances for Iran to sign the JCPOA and chose the path of nuclear restraint. These findings support the assumptions of the domestic-and norm model while putting the importance of the security model in question.Iran ́s continued nuclear restraint relies on increasing theeconomic and politicalcostsof pursuing a nuclear weapon whiledecreasingthesecurity incentivesof having one.