The study aims to extend the existing knowledge about the dynamics of first-time participation in protest events. To tackle that puzzle we rely on extensive and innovative protest survey evidence covering 18 separate demonstrations in eight countries across nine different issues. On the individual level, age, motivation, and non-organizational mobilization appear to be consistent and robust predictors of first-timership. On the aggregate level, demonstrations staged just after or during a protest wave, large demonstrations, and demonstrations of old or new emotional movements are attended by a relatively larger share of first-timers. We conclude that it is thus the interplay of individual-and aggregate-level determinants that produces first-time participation.