Abstract: Based on Habermas normative theory of religion in post-secular society, this article elaborates on the organisation of Islamic religious education (RE) in state schools. Hereto, a brief sketch of the Habermasian concepts of reflexive religion and complementary learning processes will be given. Subsequently, the author addresses the role of RE in post-secular society and applies these Habermasian concepts to confessional RE, with particular attention to Islamic RE in Belgium, where this subject is included as an optional subject in the state school curriculum since 1975, but where it is also criticised today, in particular with regard to content, teacher-training, textbooks, and inspection. These deficiencies will lead us to one of the main problems of Islamic RE and of confessional RE in general: the absence of state control. Based on Habermas ideas, the author concludes that it is up to the state to elucidate under which conditions confessional RE can be part of the regular curriculum, and to facilitate these conditions, by funding and co-organising teacher training, reviewing curricula and textbooks, formulating a core curriculum and controlling teachers, for example. If these conditions have not been met, confessional RE should not be a part of the regular curriculum in a liberal state.