Written in a nontechnical and easy-to-follow style, the book covers what viruses are and where they come from; how they transmit and evolve; the battle between viruses and hosts, including immunity and vaccination; viruses that are good for us; the critical role viruses play in the balance of earth's ecosystems; what makes a virus - including COVID-19 and influenza—become pandemic in plants or animals; and the cutting-edge research that is discovering thousands of new viruses. Each chapter concludes with stunningly illustrated profiles that highlight key viruses.