Bioterrorism, biological weapons and the fear of intentional disease have a long history and are not new thoughts – we knew how to spread disease long before we understood the science behind it. This talk briefly reviews some of this early history, before exploring in more detail the application of microbiology to the military armaments of the twentieth century. Turning to today’s security context, I consider current threats from state-level bioweapons programmes and what we currently know about terrorists’ interest in biological weapons. I argue that we need to nuance discussions about the threat of deliberate infliction of disease, separating out small-scale attacks from sophisticated, large-scale attacks. The talk concludes by considering whether advances in the life sciences, particularly in synthetic biology and gain-of-function studies, will alter the threat equation in the near future.