The question of dangerousness -- how it should be defined and punished, and the ethical dilemmas associated with it -- is a recurring theme of modern policy and penological discourse. In this powerful book, John Pratt addresses this question by explaining how dangerousness first became an object of penological discourse and why it has remained so. The late nineteenth century was an important turning point as earlier concerns about the threat posed by the dangerous classes give way to a new set of concerns about dangerous criminals. He traces change to the present, identifying 'Three Strikes' laws and related initiatives as the latest in a long line of attempts to govern the dangerous.