This paper summarises some of the main ideas that shape the theoretical terminology of my project. It focuses on the application of the term “unbelief” in Classical Athens reflecting on the establishment of “self-world relations” at that time. This draft belongs to the final chapter of my dissertation (see the table of contents) in which I analyse some of the most relevant sources to study “atheism” in Athens during the second half of the 5th and the first decades of the 4th centuries BCE. The paper is structured in four main sections. The first one deals with Protagoras and his “agnosticism”. The second section reflects on Prodicus’ theory of religion and his connections with the so-called Sisyphus fragment. Thirdly, the paper follows some ideas developed in this fragment that resonates with Democritus’ theology. Finally, the last section focuses on Diagoras of Melos and the relationship between being “atheist” (atheos) and the crime of “impiety” (asebeia). The text concludes with some reflections on unbelief as part of the “religious individuation”.