This is a collection of papers delivered at the NATO Advanced Research Workshop of the same name, which examined the role of independent scientists inassessing WMD threat. Such threat assessment has a profound impact on the policies of governments and international organizations. With papers coveringtopics ranging from policy making to chemical and biological weapons, nuclear threats and breaking the threat or counter threat cycle, this book illuminates an area of vital importance to the security and stability of relations between states, and the maintenance of internationally agreed norms.