This essay analyses the role of religion in the Black Notebooks in the context of Heidegger's evolving attitude to both Christianity and Nazism. The introduction summarizes Heidegger's developing theology and later counter-theology of the 1910s and 1920s, which converges (as I have argued elsewhere) on the formulation of an "eschatology without eschaton" in Being and Time's central concept of being-unto-death. The first main part presents and analyses the strong anti-Christian polemics of the Black Notebooks in their biographical, institutional and philosophical contexts. The second part examines Heidegger's evolving attitude to the role of National Socialism vis-à-vis this critique of Christianity, focusing on competing appropriations of nineteenth-century secular apocalypticism by neo-Fichteans, Nazis, and Heidegger himself. The third part discusses his reconfiguration of eschatology in more detail, delineating its continuities with and departures from Being and Time's being-unto-death.