The introduction outlines key historical differences between contemporary “intersex” and “transgender” and the historical term “hermaphrodism.” Even when the binary was in many ways unquestioned, it is still imperative to look at it, perhaps even more acutely, because tiny moments of resistance forged in an environment without so much as the vocabulary needed to define that resistance are the forbearers of the present. A wealth of historiography attests to the ways in which nineteenth-century medicine labored to naturalize the distinctions between men and women, yet when doctors were confronted with cases of “hermaphrodism,” many began to realize that there were some individuals who could not be classified as one or the other, casting the entire binary into doubt. At the same time, novelists increasingly began to imagine characters who did not fit neatly within the gender binary, sometimes creating entire novels in which the mystery of a character’s gender identity actually motivated the plot. Everyone in nineteenth-century France accepted that there were differences between men and women, but for the first time both medical and literary narratives came to the surprisingly similar conclusion that determining the exact nature of those differences was excessively difficult, and even sometimes strictly impossible.