The hijackers were involved in 308 incidents committed on air carriers registered in the United States. Data were obtained from the Federal Aviation and the FBI investigative files. Findings supported a typology that included five general types of hostage takers, with one type including four subtypes. These types were the alienated immigrant, the politically motivated, the extortionist, the escaping prisoner, and the personally distressed. The personally distressed included the mentally ill, alcohol abusers, drug abusers, and personally disordered. These eight categories accounted for 96 percent of the aircraft hijackings. Results also indicated that the politically motivated group is the most important and that alcohol and drugs are extensively involved as co-factors in aircraft hijackings. Further studies will examine the typology in more detail and will also consider the duration of the event, weapons used, and operational and tactical issues. Figures and 31 references