Questions about the quality of political representation are central to research on women and gender, and to political science in general. Given a certain set of interests, how well do political institutions and political actors address and advance those interests? Research about the quality of political representation relies a priori on the existence of fixed, stable, and measurable interests; we need to know what women want before we can assess how well politicians represent them. Perfect measures of the interests that all women share have proven elusive. The measures of women's interests that scholars commonly employ lend themselves reasonably well to research, but have unfortunate side effects: They essentialize gender norms, exclude certain groups of women, or define women's interests too narrowly. In this essay, I explore the political implications of the empirical measures of women's interests on which scholars have relied in research on women's political representation. I offer a way to measure women's interests that draws upon the United Nations Convention to Eliminate All Forms of Discrimination Against Women (CEDAW). CEDAW provides a way to think about women's interests that is broad, inclusive, and sufficiently flexible to reflect changes over time. Furthermore, it enjoys the explicit approval of almost every nation in the world; 186 countries have ratified CEDAW since the UN General Assembly approved it in 1979.