Introduction: "A contagious living fluid": tobacco mosaic virus -- Old companions: The uncommon cold: rhinovirus; Looking down from the stars: influenza virus; Rabbits with horns: human papillomavirus -- Everywhere, in all things: The enemy of our enemy: bacteriophages; The infected ocean: marine phages; Our inner parasites: endogenous retroviruses -- The viral future: The young scourge: human immunodeficiency virus; Becoming an American: West Nile virus; Predicting the next plague: severe acute respiratory syndrome; The long goodbye: smallpox -- Epilogue: The alien in the watercooler: mimivirus.