Determinants of collective behavior, as suggested by the social identity or self-categorization approach and social movement research, were examined in 2 field studies. Study 1 was conducted in the context of the older people's movement in Germany and Study 2 in the context of the gay movement in the United States. Both studies yielded similar results pointing to 2 independent pathways to willingness to participate in collective action; one is based on cost–benefit calculations (including normative considerations), and the other is based on collective identification as an activist. Study 2 included an experimental manipulation and provided evidence for the causal role of collective identification as an activist. Directions for future research on the proposed dual-pathway model are suggested.