Professor Saltzman talks about the importance of vaccines, and particularly the role of bioengineering in vaccine development. He first addresses the question of "what is a vaccine" and the role of the immune system. He then describes the biological basis, symptoms, and history of smallpox as a devastating disease worldwide, and how--starting with the work of Edward Jenner--an effective vaccine was systematically developed from cow lesions. Next, methods to deliver vaccine to a wide population are introduced. Finally, Professor Saltzman touches on the possible reemergence of smallpox as weapon for bioterrorism.