As Sapiro (1981) pointed out many years ago, recognizing that women's interests are interesting is the vital first step in establishing the significance of women's political representation (or the lack thereof)—both in the “real” world and in the scholarly world. Indeed, the assumption that women's interests exist, that women have political interests that can be defined and measured, is central to much of the subsequent research and discussion of women in politics. It is central to our own research on the relationship between women's descriptive and substantive representation (e.g., Reingold 2000; Swers 2002), and it is central to this symposium. Yet we come together in this symposium not simply because we share this assumption, but more tellingly because we all grapple with this assumption. Defining and measuring women's political interests pose a number of very difficult questions or dilemmas, which we elaborate in the following. We highlight these challenges not to dismiss such endeavors as futile or necessarily misguided. Rather, we argue that the very uncertainty surrounding women's interests is what makes them so interesting.