Theories of apocalyptic government (the global polity that will govern humanity in the End Times) provide an important lens for differentiating political movements and understanding their legal and political ambitions. These theories comprise a range of questions: What is the time span of the final government—i.e., how long will humanity survive before universal annihilation? Will the final government involve separation of powers? Will its form be democratic, autocratic, socialist, or otherwise? Will it preserve the boundaries of nation-states? How will it relate to existing supranational political entities, such as the United Nations? How will the political leadership be constituted, including its mechanisms of succession? How will its administrative and bureaucratic apparatus be organized? This Article considers such questions within the Islamic context by examining four case studies: (1) the Islamic State of Iraq and Syria (“ISIS”), (2) Muḥammad ‘Īsa Dāwūd and his “Awaited Mahdi” political party in Egypt, (3) the Islamic Republic of Iran, as represented by three de facto theorists, and (4) the Ṣadrist movement in Iraq, as represented by the movement’s former leader.  While these case studies may appear to be superficially similar, their theories of apocalyptic governance and constitutional law differ markedly.