To date, no pattern of actual attacks on United States territory has emerged that provides a clear basis for predicting how serious any given form of attack will be in the future, what means of attack will be used, or how lethal new forms of attack will be if they are successful. The United States must make decisions in order to shape programs that will affect its capabilities as much as a quarter of a century in the future. One of the greatest single problems the United States faces in dealing with the threat posed by CBRN attacks is that there is no way to predict the probable nature of the threat that can be firmly rooted in either an analysis of past patterns of attack or a clearly identifiable threat from specific countries, or foreign and domestic extremists. This draft report on Homeland Defense was prepared by the Center for Strategic and International Studies (CSIS) and focuses on the current and future terrorist risk and threat to the United States. The report begins with an examination of risk assessment, specifically the planning for non-patterns and potential risk. In addition, there are two further issues that the United States must deal with in defining the threat: (1) the possible nature of the attackers, and (2) the possible means of attack. The United States needs to improve its threat and risk assessments in terms of the way in which it analyzes attackers and the ways in which they might use weapons of mass destruction. The report concludes with an examination of threat prioritization, specifically identifying current and future threats. It identifies potential state actors, foreign terrorists and extremists, and domestic terrorists and extremists. References, charts, and tables