In this paper I argue that cosmopolitanism prohibits war and requires a global approach to criminal justice. My argument proceeds by drawing out some implications of the core cosmopolitan intuition that every human being has a moral status which constrains how they may be treated. In the first part of this paper, I describe cosmopolitanism. In the second part, Cosmopolitanism and War, I analyse violence, consider the standards cosmopolitanism sets for its justification, and argue that war fails to meet them. (...) In the third part, Cosmopolitanism and Criminal Justice, I argue that cosmopolitanism implies a moral obligation to deal justly with human wrongdoing wherever it occurs. Cosmopolitan pacifism follows: war is prohibited, and a consistent global criminal justice system is required. In the fourth part, Why No Cosmopolitan Pacifists?, I consider why cosmopolitans tend not to identify as pacifists, and in the final part, Objections, I discuss some objections. (shrink)