Butler was thirty-four when she wrote the book, having just finished her PhD at Yale on Hegel. The choice of subject was personal: as the lesbian and gay movements grew in the late 1980s, the movement's working assumption that 'woman' or 'homosexual' was a fixed, natural, and inclusive category had begun to be questioned. Butler gave that questioning a philosophical ground.

The central thesis works through three main moves. First, Beauvoir's formula 'one becomes a woman' is radicalised: 'becoming' is not a process that begins and ends once; gender is a performative activity, continuously reproduced through daily acts (dress, gait, tone of voice, gesture, marriage rituals). Second, the biological 'sex' is itself culturally constructed: which bodily features count as important, how the body is sorted into binary (male/female) categories — these are not neutral natural science but historical decisions. The classical feminist distinction between sex and gender is itself problematic. Third, a normative system called the 'heterosexual matrix' (man/woman binary, man-woman desire, the formation of the family) holds the whole construction in place and naturalises it.

Butler weaves these theses with concepts pulled from Hegel, Foucault, Lacan, J.L. Austin (speech-act theory), and Derrida. The book is dense and technical; in her 1999 preface Butler admits the book is 'difficult' and apologises slightly for it. But as its theses spread, the popular formula 'gender is performative' became canonical.

*Gender Trouble* is the birth certificate of two theoretical fields: academic 'queer theory' (alongside Eve Sedgwick's *Epistemology of the Closet*, also 1990) and the contemporary understanding of gender as fluid. The book has also been heavily attacked from conservative quarters; since the late 2010s Butler has been the target of verbal and physical attacks in several countries, particularly in Eastern Europe, Latin America, and including Turkey. The contestation around the idea is itself proof of its influence.