How far can we apply the same moral principles to both public and private behaviour. In the interests of effective political action, are we right to accept acts of deceit, exploitation or force which we would regard as unacceptable in private relations with individuals? What means can be properly adopted in the promotion of great public causes? The problem of 'dirty hands' in politics was posed most strikingly by Machiavelli. It has re-emerged this century in a pressing and, to some extent, a new form, in connection with the two World Wars and more recently the Vietnam War, where the political decisions and the destruction, and risks of destruction, have been of a scale and character not previously experienced. The contributors, including Bernard Williams, Thomas Nagel, T. M. Scanlon, and Ronald Dworkin, examine the background to this problem in moral and political theory.