Negligence is a neglected topic in work on Elizabeth Anscombe’s account of action. This is unfortunate because negligence is crucial to understanding Anscombe’s general philosophy of psychology—in particular, her account of the voluntary and the role that practical self-knowledge plays in her understanding of it. Attention to negligence also helps us better understand the extent to which Anscombe’s account of human agency and action is influenced by the thought of St. Thomas Aquinas. In this chapter, I discuss Anscombe’s account of practical self-knowledge of intentional action in order to show how the account can be extended to cover the voluntary. I then apply this account of the voluntary to her treatment of negligent actions and omissions.