Most information on police deals with formal structures, authorizations, and personnel management. Information about processes and practices, especially from first-hand observation, is rare, and the descriptive materials available refer to a small proportion of the world's police. Reference books on police exist for only a few countries, primarily those in western Europe, North America, and the Commonwealth; but the information in such books, as well as in official publications, is selective. Factual information is not provided for such areas as rates of pay, tort liability, duration of training, rank stratification, recruitment qualifications, modes of deployment, budget, weapons, women in service, and functional specialization. Information is also lacking on how well police are performing, largely because police performance evaluation is rare, and where evaluations have been made, they have been flawed by the use of reported crime statistics and clearance rates, which are defective data sources for measuring police crime control performance. Better data sources are victimization surveys. The structure of command is another fundamental aspect of policing currently uninformed by analysis. Information is also needed about how society and circumstances affect the police. Information in the aforementioned areas is important for international comparisons among police. Comparison is basic to all analytic inquiry that examines the effects of policy or the determinants of action. Without multiple instances to study, generalizations cannot be substantiated. Ten notes are provided.