Decisions made by a government agency on an individual’s sex classification can differ from an individual’s understanding of themselves as female, male, or nonbinary. This disjunction has often been understood as a conflict between sex construed as a biological phenomenon and gender as a psychological/social phenomenon. This article presents another way to understand conflicts and contradictory outcomes in gender/sex classification. Instead of thinking about problems in the state management of gender/sex as consequences of getting the definition “wrong” or as disagreements about “what sex really is” and its relation to gender, this article suggests that much can be learned about the use of gender/sex in policy by adopting the methodological starting point that “sex” is not a thing in itself but only an effect of a particular state action. It focuses on one particular issue: the reclassification of an individual as female, male, or nonbinary by state actors in the United States. Examining these policies in the United States, three distinct phases are identified that reveal the different governing and political rationales at play.