There are powerful limits to international humanitarian law. With reference to theories of international relations and to empirically observable patterns, this article shows the inability of legal norms and structures to influence the behaviour of the world's most powerful states and their allies. There are also restrictions on the capacity of trials conducted according to humanitarian law to fulfil the social functions increasingly attributed to them, including the re-education of populations complicit in mass crimes, some measure of catharsis for the victims of such crimes, and the reintegration of erstwhile ‘victim’ and ‘perpetrator’ communities.