Research on political terrorism, which began in the early 1970s, faces some persistent problems. These involve defining the concept, collecting empirical data, building integrative theory, and avoiding the attribution of terrorism to personality disorders or “irrationality.” Furthermore, analysis risks being driven by events or the concerns of policymakers. Nevertheless, it is generally accepted that psychological explanations of terrorism must take multiple levels of analysis into account, linking the individual to the group and to society. Future research should critically examine the assumption that a “new terrorism” has appeared at the end of the 20th century. Analysts should also take advantage of 30 years of history to develop comparisons and developmental studies that look not only at the causes of terrorism but at changes in terrorist strategy, the termination of terrorist campaigns, government decision-making, and policy effectiveness.