The simplest living organisms on Earth, viruses are endlessly studied and yet remain a great mystery. They are the cause of many human and animal illnesses, from the numerous and common cold and flu viruses that plague us for a few days or weeks, to more insidious but treatable viral infections, such as HPV, to the most feared killer viruses, such as HIV and Ebola. In this book, readers explore the mechanics of how infections occur and what kinds of diseases arise from what types of viruses. They delve into the modern landscape of prevention and cure, including how vaccines work.