This chapter examines how the historiography of Greek religion renewed itself between 1920 and 1950. This period invested a great deal of effort in the answers that could be sought from the celebrated old sources. As the former certainties were battered from all sides, the revered voices from the past often resonated with the intensity of a battle call for renewal. Greek religion, one of the most contested domains in the reception of ancient culture, was to be solicited again and again to help imagine a new future. The chapter then considers the great changes that saw the Belle Époque study of ancient religion thoroughly transformed after the Great War, and the stakes of some of the fundamental disagreements that set influential scholars of the Interwar years against each other. Ultimately, the battle for the Greek Irrational was a search for the new foundations of modernity.