Since the isolation of the first virus in 1892 scientists have made tremendous advances by asking one question at a time and building on the answers. Dr. Levine celebrates the successes that have come from viral studies - the development of a wide range of vaccines, the eradication of smallpox, and the insights into the origins of cancer. He also examines the challenges we still face, with a series of interconnected chapters on the specific viruses behind some of our most urgent public health problems, including the viruses that cause AIDS, influenza, herpes and hepatitis.