The prospect of large scale biological weapons terrorism is dreadful. Yet the empirical record of terrorists turning to disease is scant and its consequences have been modest compared to other terrorist incidents. This chapter describes the terrorist incidents that have taken place and the state biological weapons programs that have been in place in the past. It describes rapid advancements in biotechnology that could make the potential problem more severe. The author argues that secrecy in bioweapons defense as well as possibly hidden offensive programs exacerbate the problem and could lead to weapons development through misunderstandings or mistaken intelligence. She argues for greater transparency and strengthening of the international agreements that outlaw the possession and development of biological weapons.