We study participation in right-wing rallies and counterrallies in Germany to examine strategic interactions in political movements. In the leadup to two right-wing rallies, we exogenously shift potential participants’ beliefs about the turnout at the right-wing rally and left-wing counterrally, and then measure activists’ intentions to protest. For right-wing activists, own participation and participation of peers exhibit strategic substitutability. For left-wing activists, own participation and participation of peers are strategic complements. Both groups do not, however, react to changes in competitor effort. Our evidence highlights substantial heterogeneity in the nature of strategic interactions in political movements.