This essay revisits the genealogy of Michel Foucault’s Histoire de la sexualité, and calls for a reassessment of its later volumes as politically engaged expériences in historiography. Recontextualising their work within the Essentialist–Social Constructionist debate that took place among historians and theorists of sexuality in the 1980s, I show that the relations between John Boswell, the most prominent “essentialist,” and Michel Foucault, the most prominent “constructionist,” were much more amicable and complex than commentators have previously claimed. Boswell served as a “guide” for the last three volumes of Foucault’s Histoire de la sexualité. By uncovering the considerable influence which Boswell’s supposedly “essentialising” concept of “gay” had on Foucault’s later writings and politics, I demonstrate that Foucault was not committed to the historicisation of sexual concepts, but rather to the transformation, through historiography, of present-day relations. This process, at once historiographical, intellectual, subjective, and political, is what Foucault calls expérience.