Like any other social category, the meaning and conceptual boundary of “religion” is ambiguous and contentious. Historically speaking, its semantics have been transformed in highly complex ways. What is meant by “religion” reflects the specific norms and imperatives of the classifier. This article critically reflects upon the idea of “religion” employed by Karl Marx in the early 1840s. Marx reimagined the encompassing notion of “religion,” which was predominant in his time, by privatizing it in his attempt to critique the theological foundation of the Prussian state. In this process, young Marx’s discourse siphons what is claimed to be “religious” out of the categories of “philosophy,” “science,” and “politics.” In this way, Marx constructs the realm of nonreligion where he associates his own discourse with natural reason, against the reified notion of “religion” as fantastic illusions.