Abstract: Inequalities often persist because both the advantaged and the disadvantaged stand to lose from change. Despite the probability of loss, moral indignation can lead the disadvantaged to seek to alter the status quo, by encouraging them to sacrifice their material self-interest for the sake of equality. Experimental research shows that moral indignation, understood as a willingness to suffer in order to punish unfair treatment by others, is widespread. It also indicates that a propensity to apparently self-defeating moral indignation can turn out to promote people’s material self-interest, if and because others will anticipate their actions. But potential rebels face collective action problems. Some of these can be reduced through the acts of “indignation entrepreneurs,” giving appropriate signals, organizing discussions by like-minded people, and engaging in acts of self-sacrifice. Law is relevant as well. By legitimating moral indignation and dissipating pluralistic ignorance, law can intensify and spread that indignation, thus increasing its expression. Alternatively, law can delegitimate moral indignation, or at least raise the cost of its expression, thus stabilizing a status quo of inequality. But the effects of law are unpredictable, in part because it will have moral authority for some but not for others; here too heterogeneity is an issue both for indignation entrepreneurs and their opponents. Examples are given from a range of areas, including labor-management relations, sexual harassment, civil rights, and domestic violence.