A fascinating and long overdue examination of viruses - from what they are and what they do, to the vital role they have played in human history. What are viruses? Do they rely on genes, like all other forms of life? Do they follow the same patterns of evolution as plants and animals? Frank Ryan answers these questions and many more in a sweeping tour of illnesses caused by viruses. For example, the common cold, measles, chicken pox, herpes and mumps, rubella, as well as less familiar examples, such as rabies, `breakbone' fever, haemorrhagic fevers like Ebola, and virus-induced cancers. Along the way, readers will learn about the behaviours and ultimate goals of viruses, gaining a deeper understanding of their importance in relation to the origins and the evolution of life, as well as they ways viruses have changed us at the most intimate level, to help make us quintessentially human.