It is always awkward when someone asks me informally what I’m working on and I answer that I’m trying to figure out what gender is. For outside a rather narrow segment of the academic world, the term ‘gender’ has come to function as the polite way to talk about the sexes. And one thing people feel pretty confident about is their knowledge of the difference between males and females. Males are those human beings with a range of familiar primary and secondary sex characteristics, most important being the penis; females are those with a different set, most important being the vagina or, perhaps, the uterus. Enough said. Against this background, it isn’t clear what could be the point of an inquiry, especially a philosophical inquiry, into “what gender is”.