Viruses exist in the hazy zone between the living and the nonliving. Though too small to see, they profoundly affect our lives from annoying colds to deadly Ebola. They spread invisibly from person to person and then attack humans from within. In this talk Professor Siegel will address the basic question of “What is a virus?” and look at the special properties that distinguish virus from more conventional life forms as well as those features which viruses and humans have in common. We will walk though the typical strategies that viruses use to expand their numbers and to thwart the immune system and look at some of the tools at our disposal for combating these devious predators.