This chapter examines the concept of actus reus as a basic, essential component of criminal liability. It considers a range of recent scholarly interpretations of actus reus and the extent to which they are supported in the case law, with particular reference to the Canadian and U.S. jurisprudence. It discusses minimalist and maximalist interpretations of actus reus, the first of which conceives of actus reus on the basis of whatever the legislature has decided to criminalize and the second of which restricts criminal liability to positive acts. The chapter looks at approaches that interpret actus reus based on two factors: a person’s “control” over the prohibited outcome or conduct, proposed by Husak, and the person’s practical reasoning, proposed by Duff. The chapter argues that both minimalist and maximalist views of actus reus conflict with well-established features of the criminal law.