This chapter argues that the role of religion in the political and social dynamics of the Weimar Republic was determined by two axes of confessional conflict. Alongside the Catholic–Protestant antagonism, there were also significant tensions between secularism and Christianity. Both axes contributed to the formation of different social milieus during the Kaiserreich and supported their continued articulation during the Weimar Republic. The chapter explores developments within the milieus, such as the significant growth and radicalization of freethought within the socialist and communist parties, as well as the shifting relationships between them, which created a fractured and complex set of political struggles, compromises, and alliances. T...