Henry Rousso warned that the engagement of historians as expert witnesses in trials, particularly highly politicized proceedings of mass crimes, risks a judicialization of history. This article tests Roussoâ€™s argument through analysis of three quite different case studies: the Frankfurt Auschwitz trial; the Extraordinary Chambers in the Courts of Cambodia; and the International Crimes Tribunal in Bangladesh. It argues that Roussoâ€™s objections misrepresent the Frankfurt Auschwitz trial, while failing to account for the engagement of historical expertise in mass atrocity trials beyond Europe. Paradoxically, Roussoâ€™s criticisms are less suited to the European context that represents his purview, and apply more readily to the highly-politicized crimes tribunals outside the continent. Finally, it contends that the importance of the proceedings themselves should be measured in full against the hypothetically corrupting effects of historiansâ€™ engagement as experts in court.