We study the relative effectiveness of exit (divestment and boycott) and voice (engagement) strategies in a world where companies generate externalities and some agents care about the social impact of their decisions. We show that if the majority of investors are even slightly socially responsible, voice achieves the socially optimal outcome. In contrast, exit does not unless everybody is significantly socially responsible. If the majority of investors are purely selfish, exit is a more effective strategy, but neither strategy generally achieves the first best. We also show that exit can sometimes reduce social welfare.