This essay addresses one of the central questions in the ongoing debate about just war theory: are soldiers morally responsible for serving in unjust wars? Francisco de Vitoria addressed this question in the sixteenth century using the concepts of invincible and vincible ignorance. He excused soldiers serving in unjust wars, if they did not know the war was unjust and if they did not have the means to overcome their ignorance; if they had the means, they were morally culpable. In (...) modern just war theory, ignorance is still used both to blame and excuse military service in unjust wars. This essay identifies ten different ways that scholars have used ignorance to argue about the moral responsibilities of soldiers. It then applies the different meanings of ignorance to soldiers serving in Western nations and, using Vitoria’s means tests, evaluates if modern soldiers do indeed have the means to overcome their ignorance. Since many soldiers do have the means, invincible ignorance should no longer be used as an excuse for their service in unjust wars; furthermore, soldiers may, in fact, be morally culpable for serving in them. (shrink)