Everyone is aware of the COVID-19 virus and the pandemic that it is causing. But what exactly are viruses? How are they different from bacteria and other parasites? How do they infect, replicate, spread, cause illness and even kill? Why are they so hard to treat? Where do they come from? How do they evolve? Are viral pandemics inevitable? In this course, I will address these and other issues; although many questions will, alas, remain unanswered.