The book that reoriented feminist and queer theory around the claim that gender is not an expression of an inner truth but a performance sustained by repetition. Judith Butler argues that the feminist appeal to "women" as a stable political subject is self-undermining, because the category is produced by the very power structures feminism seeks to contest. Drawing on Foucault, Lacan, Wittig, and a close reading of Simone de Beauvoir, Butler dismantles the familiar division between biological sex and cultural gender, contending that sex itself is already a cultural interpretation and that the appearance of a natural, prediscursive body is an effect of the system rather than its foundation. The book's central concept is performativity: gender exists through the reiterated stylization of acts, gestures, and desires that, through repetition, congeal into the illusion of a natural essence. Butler's discussion of drag is the most cited and most misread passage, since the point is not that gender is a costume freely chosen but that drag exposes the imitative structure of all gender, including the kinds that pass as original. Dense, polemical, and written in a prose style that has itself been the subject of decades of argument, Gender Trouble has shaped work across philosophy, literary studies, anthropology, and politics. Butler's later preface addresses the misunderstandings directly, clarifying that the aim was never to prescribe a new way of living gender but to widen the field of what a livable life can include.