AbstractInformal social sanctions such as ostracism are the primary means of controlling deviance in communities. Formal legal sanctions are a costly back-up. Yet outside of university laboratories, studies of ostracism barely exist. We examine legal cases brought by targets of ostracism in Japan, encompassing nearly all the non-trivial reported opinions. The cases do not involve villagers who actually offended their community. Instead, most plaintiffs are victims of opportunistic ostracism, where ostracism is used to extort property, hide community-wide malfeasance, or harass rivals. We explore carefully the non-random character of the disputes and provide a formal model in the annex. We conclude that typical plaintiffs in these lawsuits are not seeking to harness the government's coercive power. Instead, they bring suit for the informational role of courts, aiming to have the court publicly certify that they did not misbehave, contrary to what ostracism might be thought to imply. This analysis contributes to the growing body of legal scholarship on social norms and the role of the courts as informational intermediaries.