There is no shared definition of police science. What exactly is police science? Should it be limited to the engineering of police methods and organisation? And how could progress towards science in policing be made when we have no definition of the police themselves, of the object or subject of the science? What are the police? Are they just the ones that claim ‘we arein a given country at a given time, as typically do public national forces in continental Europe? This really seems a very empirical and conceptually week definition of police that might not be sufficient for establishing them as an object or subject of a science. Forging a comparative methodology for studying ‘police’ requires scholars to discuss and perhaps agree about the key notions that can guide empirical works and to develop names for and measures of the various dimensions that constitute ‘police’.