Abstract: In this lecture, I will explore the significance of materiality and material turn in the study of religions for understanding religious change and transmission during communism and the indispensable nature of the secret police archives for this endeavour. Based on the findings of the Hidden Galleries ERC project, which focused on the archives of the secret police in Hungary, Romania, Moldova and Ukraine, I suggest ways in which the insights and methods employed by scholars of religions can help us access the agency and creativity of religious communities under surveillance, and in so doing reveal the processes of religious change that have helped shape contemporary Central and Eastern Europe. I will present the multi-layered, hybrid assemblage of texts, items and images that were gathered by the communist-era secret police as incriminating evidence and suggest ways in which these materials become “evidential” for the study of religions under communism.