The need to talk about and establish boundaries is perhaps stronger in relation to the criminal law than any other area of law. The field of criminal law marks itself out by its history of preoccupation with limits – of the law, of the sanction, of criminalisation. These images of space and landscape continue with descriptions of the contours of liability, the field of punishment, the frontiers of criminality, or the territory of the law. It is thus appropriate that we should begin with a passage from Blackstone's Commentaries that recognises, in a particularly elegant manner, the significance of boundaries and divisions. It is rarely referred to now, but Blackstone's exposition of the common law of crime has been of enduring importance to modern ideas about the law.