Bacteria and viruses are among the oldest agents on Earth and reveal much about the planet's past and evolution. As scientists and doctors make progress in fighting the harmful effects of bacteria and viruses, they also often make discoveries that can lead to life-saving vaccines and antibiotics, making the fields of microbiology and biochemistry more intriguing and challenging than ever. In this volume, readers will venture into the realm of bacteria and viruses to explore these constantly changing agents and the roles they play in nature, medicine, and disease.