Michel Foucault is the first philosopher who develops a complex notion of "archive". Nevertheless, this concept is usually identified only to the propositions held in Archaeology of knowledge. The present work aims at arguing that the particular concept of archive developed by Foucault may be traced along his entire work, this is to say, it can be found along his different stages: archaeological, genealogical and ethical. Our thesis, therefore is that the notion of archive has been until now, an often forgotten key to the understanding of Foucault's political and philosophical thought.