Germs get a bad press, so we never hear their side of the story. What is life really like in their invisible kingdom? Arno Karlen tells the fascinating life story of the germ Borrelia burgdorferi (Bb for short), the microbe that causes Lyme disease. He takes us through its ancestry, its appearance, its environment, its sex life, its struggle for survival, and its adventures with other species, including us. Interwoven with Bb's biography are fascinating discursions on how life began, why we cannot live without bacteria, and how perturbed environments breed disease. Karlen also describes how perceptions of microbes have changed through history, especially their unfair connection with dirt and suffering. The Biography of a Germ makes the world of microbiology absolutely riveting, and it will help to rehabilitate Bb's undeserved reputation.