Abstract: It is commonplace to think that a person can be morally responsible for an unwitting wrongful action if she is culpable for her ignorance. Some philosophers, including Thomas Aquinas and Kevin Timpe, argue also that a certain kind of non-culpable ignorance—namely, concomitant ignorance—also can ground moral responsibility. An agent is concomitantly ignorant with respect to wrongdoing if the agent is non-culpably ignorant that the action is wrong, but she would have freely performed the wrongful action anyway if she were not ignorant. I argue that concomitant ignorance cannot ground moral responsibility, and so differs from culpable ignorance in this respect. I explain why choice-based and character-based accounts of moral responsibility plausibly preclude concomitant ignorance from grounding moral responsibility, and then offer several explanations for why some philosophers mistakenly believe that concomitant ignorance preserves moral responsibility.