Our world is swarming with invisible organisms - bacteria and fungi that affect their hosts and environments in diverse ways. This text looks at the mysterious microscopic world of microbes and investigates how they behave, and why. It tells stories of how scientists have discovered the laws of behaviour of the world of microbes, including the principles of locomotion, navigation, survival, reproduction and communication. In addition, the text relates the behaviour of bacteria and other microbes to our more familiar world and shows their impact on our lives.