This paper explores how party-specific contextual factors explain variations in membership levels. Based on a subset of MAPP data that includes 2898 yearly membership data points for 262 parties in 24 countries over a period from 1990 to 2014, it examines three sets of explanations: the lifecycle model (party age), the bandwagon model (electoral performances and governemental participation), and the competition model (effective number of parties). Our results confirm that membership ratios present an overall decreasing trend across parties over time. At the same time, we show that this trend is flattening and that there are important variations across parties. Fluctuations of membership are part of a party’s lifecycle. Our results also point toward a bandwagon effect whereby party membership levels increase or decrease according to electoral performances, and to a patronage boost linked to governmental participation. Finally, we show that party system fragmentation decreases individual parties’ membership ratios. Overall, our findings complement the story on party membership decline and calls for further investigations of party-specific explanations.