Based on a unique panel data-set of actual voter turnout covering 58 ballots and 12 years in the canton of Geneva, Switzerland, we analyze political participation from a longitudinal and contextual perspective. Focusing on a small number of individual sociological factors we hypothesize about how the impact of these factors varies over time and as a function of different institutional ballot characteristics. By applying multilevel models for growth, we find suggestive evidence for three age effects: period, aging, and cohort. While the data exhibit the expected convergence in turnout between Geneva and non-Geneva citizens over time, the results suggest that women had already caught up with men by the beginning of our study. The results are less straightforward, but not less interesting, with regard to institutional variables, which interact with age, but not with sex or citizenship status.