Standard accounts of the ideological basis of secularization tend to focus on the emergence of non-religious justifications of the authority of the state in early modernity. This article argues that successful secularization also requires a certain political theology, one that leads religious believers to accept that the rules of their religion cannot justifiably claim the status of public law. This thesis is developed through an in-depth account of Hobbes's political theology in books III and IV of Leviathan. It is also argued that Ernst-Wolfgang Böckenförde's reflections on the process of secularization and on the proper relationship between church and state can be read as offering a contemporary version of Hobbes's political-theological argument.