Several areas of rapid technical innovation, such as biotechnology, nanotechnology, and neuroscience, offer great promise for human health and welfare but could also be exploited for the development and production of biological or chemical weapons. Such technologies pose a ‘dual-use dilemma’ because it is difficult to prevent misuse without foregoing beneficial applications. Indeed, in many cases the technologies that can do the most good are also capable of the greatest harm. Since the terrorist attacks of September 11, 2001, several developments in the life sciences have raised the political salience and urgency of the dual-use issue. One example is the synthesis from scratch of several pathogenic viruses, including the causative agents of polio, SARS, and the 1918 pandemic strain of influenza.