Using survey data from a representative sample of adults in the United States, this article examines the effects of grievances and voluntary organizational membership on protest invitation and protest participation. Instead of comparing protestors to non-protestors, it looks at protest participation as a two-step process. First, people are invited (or not) to protest. Second, they accept (or not) the invitation. The article shows that aggrieved individuals are more likely to be invited to protest. Yet grievances do not have a significant direct effect on protest participation. Membership in political, collective identity, and community service organizations increase the likelihood of being invited to protest. But only political organizations contribute to protest participation after controlling for the effect of protest invitation.