The Iranian regime has assembled a large toolbox to deter military, economic, and political challenges and threats. The foundation of this deterrence system is a large arsenal of missiles built in Iran and in the possession of Shiite militias, most prominently, Hezbollah. The militias are designated for land warfare against Iran’s adversaries; Iran’s large naval array threatens shipping and oil exports in the Persian Gulf. Nuclear capability would compound Iran’s deterrence, even if Tehran is in no hurry to use it. Consequently, even Iran’s powerful adversaries, including the United States and Israel, avoid steps liable to lead to large-scale conflict. Nonetheless, there are weak points in Iran’s deterrence system. Realizing the superiority of the US military, the regime too is careful to avoid large-scale conflict. Iran has no solution for the heavy economic pressure leveled by the US or for the Israeli attacks on Iranian and Shiite targets in Syria. It recoils from using its missile system against the US and Israel, except on a limited scale. The killing of Qasem Soleimani and Mohsen Fakhrizadeh demonstrate that Iran faces difficult deterrence challenges.