The objective of this chapter is to clarify the social theory underlying in Foucault’s genealogy of power/knowledge thanks to a comparison with Tarde’s microsociology. Nietzsche is often identified as the direct (and unique) predecessor of this genealogy, and the habitual criticisms are worried about the intricate relations between Foucault and Marx. These perspectives omit to point to another – and more direct – antecedent of Foucault`s microphysics: the microsociology of Gabriel Tarde. Bio-power technologies must be read as Tardian inventions that, (...) by propagation, have reconfigured pre-existing social spaces, building modern societies. We will see how the Tardean source in Foucault’s genealogy sheds new clarity about the micro-socio-logic involved in it, enabling us to identify some of its aporiae and to imagine some solutions in this respect as well. (shrink)