The expansion of women's formal political representation ranks among the most significant trends in international politics of the last 100 years. Though women made steady political progress, substantial country-level variation exists in patterns of growth and change. In this article, longitudinal theories are developed to examine how political factors affect women's political representation over time. Latent growth curve models are used to assess the growth of women in politics in 110 countries from 1975 to 2000. The article investigates how electoral systems, national-level gender quotas and growth of democracy – both political rights and civil liberties – impact country-level trajectories of women's legislative representation. It is found: first, national quotas do affect women's political presence, but at a lower level than legislated by law; second, the impact of a proportional representation system on women's political representation is steady over time; and third, democracy, especially civil liberties, does not affect the level of women's political representation in the earliest period, but does influence the growth of women's political representation over time. These findings both reinforce and challenge prior cross-sectional models of women's political representation.