Women's low rate of participation at the highest levels of politics is an enduring problem in gender stratification. Previous cross-national research on women in national legislatures has stressed three explanations for differences in women's political representation: social structure, politics, and ideology. Despite strong theory suggesting the importance of ideology, it has not found support in previous cross-national statistical studies. But ideology has not been as well measured as structural and political factors. In this article, we demonstrate that gender ideology strongly affects the number of women in national legislatures. We do so by introducing a newly available measure of national gender ideology into a cross-national model of women in legislatures. We demonstrate that ideology, when measured more precisely, strongly predicts differences in women's political representation.