This Article argues that the anti-stereotyping theory undergirding the foundational sex-based equal protection cases of the 1970s, most of which were brought by male plaintiffs, has powerful implications for current controversies in sex discrimination law which have long been obscured by the dominant narrative about these cases. For decades, scholars have criticized Ruth Bader Ginsburg for challenging the constitutionality of sex-based state action in cases featuring male plaintiffs. They have argued that the predominance of male plaintiffs caused the Court to adopt a narrow, formalistic conception of equality incapable of rectifying the subordination of women. This Article offers a new account of the theory of equal protection animating Ginsburg’s campaign. It argues that her decision to press the claims of male plaintiffs was grounded not in a commitment to eradicating sex classifications from the law, but in a far richer theory of equal protection involving constitutional limitations on the state’s power to enforce sex-role stereotypes. This “anti-stereotyping” theory drew on the arguments of transnational movements for sex equality that emerged in the 1960s, including the movement to combat sex-role enforcement in Sweden and the women’s and gay liberation movements in the United States. The Burger Court incorporated the anti-stereotyping principle into sex-based equal protection law in the 1970s, but the significance of this doctrinal shift has long been overlooked, in part because the Court initially applied the new doctrine only in a limited set of domains. In recent years, the Court has extended anti-stereotyping doctrine beyond the provisional limitations established in the 1970s and in ways that are deeply relevant to questions at the frontiers of equal protection law today.