Prior research shows that members of voluntary organizations are more likely to protest than nonmembers. But why, among members, do some protest while others do not? I explore whether organizational involvement—the extent in which members engage in the “life” of their organizations—affects protest. I identify four dimensions of involvement—time and money contributions, participation in activities, psychological attachment, and embeddedness in interpersonal communication networks. Only the first dimension has robust effects on protest, and they are nonlinear: intermediate contributors have the highest protest rates. The three other dimensions substantially increase protest only under specific “involvement profiles.”