This chapter considers the alternative argument that soldiers who fight in criminal wars are “invincibly” ignorant of the wrongfulness of their acts. Although superficially attractive, this theory presumes implausible moral standards that contradict pervasive legal principles. It is true that few soldiers know their wars to be criminal, but it is also rare that soldiers fighting in illegal wars have good reasons to believe those wars to be lawful. Domestic criminal law, the jus in bello, and the jus ad bellum all hold it to be wrongful to inflict violence intentionally when uncertain as to whether the justificatory conditions for doing so obtain. Moreover, three factors undermine the soldier’s grounds for presuming the reliability and honesty of her state’s official position on the jus ad bellum status of a war: multiple, countervailing epistemic authorities; the interestedness of the soldier’s leaders; and a global history of state mendacity and mistake on jus ad bellum facts. If there is a general epistemic argument for deference, it supports deferring not to the soldier’s own state, but to the preponderance of uninterested and neutral states and international organizations.