This chapter sets out in more detail two concepts of responsibility, “moral” and “ascriptive”, as they are used in this book. Moral responsibility is concerned with a defendant’s eligibility for moral praise or blame in respect of her behaviour. Ascriptive responsibility, by contrast is concerned with the conditions of accountability. The latter is audience-relative: the former is not. Within the criminal law, denials of moral responsibility are accommodated through defences such as infancy and insanity, and by the requirement of voluntariness. Denials of ascription, by contrast, turn primarily upon doctrines of causation, omissions, and complicity. The chapter concludes with a critique of the so-called voluntary act requirement.