Between 1966 and 1971 Michel Foucault's philosophy moves from the paradigm of archaeology, present in his well-known work as Les mots et les choses and L'archéologie du savoir, to that of genealogy, influenced by authors like Nietzsche and Deleuze. The problem of historical knowledge stands at the center of this transformation. This essay tries to account this shift in Foucault's philosophy from the point of view of the event: from its «regulated use» in the archaeological method, which involves in a new synthesis structuralism and the so called histoire sérielle, to the nietzschean genealogy in which the singularity of the event jeopardize the concept of history as such.