Sex is documented, administered, and adjudicated via a network of statutes, regulations, and administrative rules that is astonishing for both its inconsistencies and its complexity. (1) Courts and agencies tasked with issuing identity documents, or determining who qualifies as a spouse for the purposes of marriage licenses or same-sex marriage bans, routinely adjudicate the question of sex--employing "common sense" approaches to determine whether a person is "male" or "female." (2) For transgender persons seeking new drivers' licenses or other forms of official recognition, (3) the folkways of sex can be particularly dire because courts have naturalized both the idea of binary sex and the impossibility of sex reassignment. In refusing to recognize a transgender woman as a legal woman, a Texas appeals court exclaimed, "There are some things we cannot will into being. They just are." (4) The Kansas Supreme Court followed suit, stating: "[W]e recognize that J'Noel has traveled a long and difficult road. J'Noel has undergone electrolysis, thermolysis, tracheal shave, hormone injections, extensive counseling, and reassignment surgery. Unfortunately, after all that, J'Noel remains a transsexual, and a male." (5) Yet, despite our collective belief in the inevitability of sex and the categories "male" and "female," sex identities evade binary categorization and neat, tidy description even at the level of biology. Every year, thousands of infants are born intersex, with bodies that fuse the chromosomes, hormones, gonads, g******s, internal sex organs, and secondary sex characteristics typically thought to be defining of "male" and "female." (6) Every year, thousands of adults also seek to change their sex--resisting the notion that sex is fixed and accurately determined at birth. (7) In addition, even those who grow up secure in their identities as "male" or "female" are assigned to a sex category, not by karyotyping, (8) but by cursory inspection of their g******s at birth, so that their anxious parents can know whether to swaddle them in a pink or blue blanket.