Women continue to be underrepresented in politics. A contemporary focus on inequality, however, belies the remarkable changes that have occurred in women's political representation, participation, and impact over time. Thus, scholars are increasingly calling for longitudinal theory and research that focuses on change across time. In this essay, we advocate moving to a longitudinal approach, which, we argue, has four broad implications for theories on women and politics. First, in shifting from a static to a longitudinal perspective, we may find greater support for existing theories that have to date generated only weak or mixed empirical evidence. Second, in contrast, we may also identify limitations of documented findings, which may not generalize broadly across time. Third, some theories imply over-time processes but have never been modeled as such. Thus, a longitudinal approach promises new, and potentially more rigorous, hypothesis testing of existing theories. Finally, theorizing over time may generate new explanations for stasis, growth, or decline in women's political representation or participation that have not, to date, been considered.