<p>In Fundamentals of Criminal Law: Responsibility, Culpability, and Wrongdoing, Simester notes that one of the basic principles of criminal law is the idea that criminal liability requires, at a minimum, moral responsibility: defendants cannot be criminally liable for something unless they are morally responsible for it. For example, we cannot be held liable for harmful consequences of involuntary behaviors such as muscle spasms, reflexes, seizures, episodes of sleepwalking, etc., for which we are not morally responsible. Simester embraces this basic assumption; however, he also challenges some standard assumptions about moral responsibility itself—in particular, he challenges the standard way of understanding the relationship between moral responsibility, voluntariness, and agency—and argues for an alternative view. This paper is a critical examination of Simester’s arguments and thoughts on this important topic. I pinpoint some ways in which I think his arguments are on target, and other ways in which I think they might not be. Where it helps illuminate the discussion, I draw connections with the philosophy of action and moral responsibility literatures.</p>