The first section of the report contains an agenda and participant list, biographies of roundtable members, and the proposal by the National Research Council's Committee on Law and Justice that led to the convening of the roundtable. The report then presents addresses and research papers from Meeting 4 of the roundtable, which focused on risk communication for terrorism. The first paper details the features of a model that guides a systems analysis designed to set priorities for terrorist threats, which in turn guides the development of appropriate counterterrorism tactics. Another paper addresses the importance and implementation of communication measures that will guide public and expert behavior and decisionmaking in the midst of the psychological impact of potential and actual terrorist attacks. A third paper examines the dynamics of collective behavior in times of crisis. The author notes that collective behavior in time of crisis need not be impulsive, irrational, and maladaptive. Responsible and rational behavior by the public in times of crisis can be assisted through credible, insightful, and well-researched communications that provide guidance. A fourth paper identifies the importance and techniques of managing a "patient surge" in association with a bioterrorist attack that includes people whose perceived ills stem from the psychological trauma precipitated by the attack. The use of information technology to implement the widespread use of health risk self-assessment tools is proposed and described. The remaining two papers present The World Health Organization's recommendations for mental health and social interventions in the event of biological and chemical attacks, as well as a paper on reactions to societal trauma. In addition to the aforementioned research papers, this report contains addresses on risk analysis for terror risk communications, the content of risk communication, biopsychological dimensions of biodefense and public health preparedness, and the long-term impacts of terrorist threats and events.