The use of informers is morally problematic for police institutions, for investigation managers, and for those individuals either who act as informers or who have daily responsibility for handling informers. This paper examines the moral issues concerning informers at each of these levels. Recourse to informers can be accommodated within Miller and Blackler's moral theory of policing. Within this context, criteria for the morally justifiable deployment of informers are proposed and supplemented with further proposed criteria for morally justifiable informer participation in crime. Morally justifiable recruitment of informers is also considered. Despite directly serving the purpose of policing, informers do not incur police professional obligations.