Traditional crimes, such as holdups and muggings, are now committed by highly moblie criminals who can vanish from the crime scene before being seen, much less identified, thereby thwarting police pursuit and arrest. Crime prevention measures are hindered by the unpredictability of a new breed of young criminals, who strike wantonly without any recognizable time, place, or motive patterns. Moreover, these criminals are more aggressive than their earlier counterparts. Terrorism and other political crimes, riots, kidnappings and hostage taking, hijackings, organized crime, international brigandage, and new types of fraud, are now handled by highly trained and specialized police personnel. The new strategies adopted by the French police include consolidation of personnel and opertions; surveillance of high-crime or target areas, access to computerized criminal histories and automated modus operandi data banks; special weapons and the latest police equipment. However, in the final analysis, police effectiveness depends on the ability of its agents to decide how and when to intervene. Preventive intervention may prevent not only the crime, but also the detention of its perpetrators, because criminal intent is hard to prove in court; simultaneous intervention entails a high risk of bloodshed; and post-facto intervention provokes public outcries of police slowness and inefficiency. Unfortunately, police officers are neither omniscient nor ubiquitous. They are only human beings who need help from their fellow citizens to identify and apprehend criminals. Illustrations are provided.