Summary: The most recent debate, like the most recent researches about society and religion in Europe, had to deal with some phenomena called «ambiguities of secularisation».  The transformations of religion in society become more and more evident than the simple crisis of religiousness, religious ideas, religious institutions or organisations. We have to choose –for the future of the sociology of religion- between the mere the description of religious change and the re-articulation of conceptual framework. In the second case we need a theory which renders possible a sociological representation of a (i) not linear and (ii) unlimited process of modernisation in which (iii) the religious actors (the churches too) can play an active role, sometimes successfully. Niklas Luhmann’s theory of society’s primary functional differentiation offers good gudelines in this last direction.