The author of a New York Times article entitled “On Being Male, Female, neither or both” concluded her comments with the following statement: “The definition of sex was (and is) still up for grabs.” In our post-modern world, we have become accustomed to the malleability of gender identity and sexuality. We are also aware that individuals undergo sex reassignment surgeries but by large we assume that transgender people are transitioning from one discrete category to another. Queer activists certainly challenge this assumption, preferring to envision sex, gender, and sexuality on a continuum, but these days even scientists don’t concur about a definitive definition of sex. Should sex be defined chiefly by anatomy? Chromosomes? The body’s ability to produce and respond to hormones? If the boundaries of biological categories can be contested, what are the implications for culturally constructed ideas about gender identity and sexuality?