The book analyses under what conditions was it possible to develop scientific atheism which was by the contemporaries in the Soviet Union and Czechoslovakia understood not only as a branch of propaganda but as a specific scholarly discipline. It maps out not only the state of affairs before the organisational changes allowed the emergence of research but also analyses the motivation which led the historical actors to make such decision in both national contexts. One of the key findings is undoubtedly the fact that scientific atheism developed as a new type of thinking about religious phenomena within the context of Marxist-Leninist epistemological doctrine. Moreover, if the socio-political conditions were favorable, it also contributed to the rethinking of the key aspects of Marxist doctrine. The comparative analysis allows to draw conclusions about the existence of specifically Soviet and Czechoslovakian scientific atheism and questions the level of sovietisation in this context.