Abstract: Informal social sanctions such as ostracism are most communities’ primary means of controlling deviance, with formal legal sanctions a costlier backup mechanism, but outside university laboratories, studies of ostracism barely exist. We construct a formal model and examine legal cases brought by targets of Japanese village ostracism. Villagers truly offending against social welfare do not bring these suits. Rather, much ostracism is opportunistic -- to extort property, hide communitywide malfeasance, or harass rivals. Typically, the objective is not to employ government’s coercive power, but to have the court publicly certify that the target of ostracism is not really culpable.