Sometimes ignorance is a legitimate excuse for morally wrong behavior, and sometimes it isn’t. If someone has secretly replaced my sugar with arsenic, then I’m blameless for putting arsenic in your tea. But if I put arsenic in your tea because I keep arsenic and sugar jars on the same shelf and don’t label them, then I’m plausibly blameworthy for poisoning you. Why is my ignorance in the first case a legitimate excuse, but my ignorance in the second case isn’t? This essay explores the relationship between ignorance and blameworthiness