The U-shaped trajectory of women’s parliamentary representation in Central and Eastern Europe over the post-communist era has generated interest among scholars and non-governmental organizations. One particularly interesting case of the recent increase in women’s parliamentary representation can be found in the Czech Republic. After the initial post-communist drop in representation, the proportion of female members of parliament (MPs) hovered around 15 percent for nearly 15 years. However, in the 2010 parliamentary election, something happened. After years of little change, the percentage of women MPs jumped from 15.5 percent to 22 percent. What caused this increase? Here, we conceive the 2010 elections as a "natural experiment" and discuss the primary factors that produced such an increase: the change in preference voting rules, activities of non-governmental organizations, and the political context surrounding the election. To test the effectiveness of these factors, we carry out a multi-method research design based on original data. We find that the reduction in the preference vote share threshold required to move up the ballot benefitted female candidates more than men in the 2010 election.