From HIV to influenza, the battle between infectious agents and the immune system is at the heart of disease. Knowledge of how and why parasites vary to escape recognition by the immune system is central to vaccine design, the control of epidemics, and our fundamental understanding of parasite ecology and evolution. As the first comprehensive synthesis of parasite variation at the molecular, population, and evolutionary levels, this book is essential reading for students and researchers throughout biology and biomedicine. The author uses an evolutionary perspective to meld the terms and findings of molecular biology, immunology, pathogen biology, and population dynamics. This multidisciplinary approach offers newcomers a readable introduction while giving specialists an invaluable guide to allied subjects. Every aspect of the immune response is presented in the functional context of parasite recognition and defense - an emphasis that gives structure to a tremendous amount of data and brings into sharp focus the great complexity of immunology. The problems that end each chapter set the challenge for future research, and the text includes extensive discussion of HIV, influenza, foot-and-mouth disease, and many other pathogens. This is the only book that treats in an integrated way all factors affecting variation in infectious disease. It is a superb teaching tool and a rich source of ideas for new and experienced researchers. For molecular biologists, immunologists, and evolutionary biologists, this book provides new insight into infectious agents, immunity, and the evolution of infectious disease.