The developed nations of the world hold an asymmetric advantage in the fight against terrorism - an advantage due to a well-funded and highly capable science and technology enterprise. This enterprise has been deployed over the past 50 years in part to support the military establishment, with incredible success. However, the basic way of thinking about military science and technology does not hold for the civil operational environment, and hence it should not be assumed in general that military technologies can simply be transferred to the homeland security community. In fact, that rarely if ever happens successfully. Furthermore, there are substantial policy constraints and issues surrounding the development of a homeland security research and development community. These issues led to the formation of a separate and dedicated homeland security research and development capability. A specific and critical issue associated with homeland security, and its research and development capability, surrounds the use of weapons of mass effect. Understanding the risks and prioritising among these threats brings additional difficult issues to the table that may never be resolvable. In part because of these very difficult policy dilemmas, the new Department of Homeland Security (DHS) was created, with a Science and Technology Directorate that is on equal status with the other operational agencies within the Department. This status reflects the President's vision for employing the advantage held in science and technology against the threat of catastrophic terrorism.