This article focuses on the concept of “biopower” and tries to explain it by its historical and methodological contextualization. Through the analysis of Foucault’s work, I define “genealogy” as a philosophical inquiry into the present, which is basically a fictional narration, built through a strong knowledge of historians’ works. The analysis of historiographical sources of Foucault’s work leads to a series of political and historiographical controversies that belong to the French intellectual field of the seventies: the theory of demographic transition and its influence on historians, and the debates on the origins of contraception and their relationship with the international population policy. My aim is to highlight the positions of Foucault on these issues, showing how through the “fiction” of biopower, he seeks to denaturalize these debates by explaining their common assumptions, including the belief that sexuality is an expression of a “nature.”