Terrorism is defined as the method by which groups seek to achieve their aims through the systematic use of violence. Both extreme right-wing and left-wing political groups use terrorism to achieve their aims. Two types of terrorists are identified. Lone terrorists are often psychotic, fanatic losers who are suicidal and possessed by fantasy images. Terrorists operating in groups are also fanatical, but posess greater discipline and lack fantasy motivation. Most American terrorists are young upper middle-class individuals with college educations, and are frequently female. Terrorists seek either to overthrow established government or seek the maintenance of the status quo. The police, as a highly visible instrument of government, are often singled out for attack; multinational corporations also are often targeted. However, the police should not yield to the temptations of eliminating due process procedures in attempts to solve terrorist crimes. Mobility, professionalism, and coordination are terrorists' strengths; lack of funds, small size, and the need to seek publicity constitute their weaknesses. Successful police operations represent one of the best ways to weaken terrorist organizations by disproving their claims that the government cannot provide protection to citizens. Investigation should emphasize agency coordination, immediate response, forensics, media coordination, and scientific analysis. The United Nations should define the term terrorist and categorize terrorists separately from political dissidents, eliminate sanctuaries for skyjackers, return terrorists to the scene of their crimes for trial, and eliminate discussions of causes from negotiations with terrorists. Police departments should improve intelligence-gathering mechanisms, encourage and assist in developing improved security systems, improve investigative capabilities, and develop higher levels of professionalism to avoid public hostility and reduce sympathy for terrorists.