A comprehensive and richly illustrated introduction to the world of viruses. As parasites that are often hundreds of times smaller than bacteria, viruses exist in and on everything, everywhere. Rapidly evolving, they are highly opportunistic and relentlessly efficient. While some viruses are obviously agents of disease, as the COVID-19 pandemic has reminded the world only too well, others can be beneficial, helping to protect their hosts from other microbes, or allowing hosts to function in otherwise impossible ways. In Viruses, virus expert and author Marilyn Roossinck presents a comprehensive and richly illustrated introduction to viruses that reveals their true nature. Using lively text, clear graphics, and beautiful imagery, Viruses examines all the aspects of viruses that are essential for understanding them—their diversity, behaviors, life cycles, and much more. 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. In a world where understanding viruses is more important than ever, Viruses offers a rich and inviting introduction to organisms that, for all the harm they can do, are also essential for the health of animals, plants, and the world we share.