How are polar bears related to pandas? For thousands of years, philosophers and scientists have tried to organize and understand, or classify, the relationships among Earth's animals and plants. Early classification systems were cumbersome and inconsistent. In the late 1720s, Carl Linnaeus began developing a classification system to describe relationships among all living things, including animals, plants, fungi, and bacteria. This organization, called the tree of life, is still the basis of the classification system used by scientists today. Recent scientific discoveries—such as the ability to decode DNA, the chemical code shared by all living things—have given biologists new insight into the tree of life. As new species are discovered and new information about old species is unearthed, the classification system continues to change. This book tells the story of how the science of classification has revolutionized the way we look at life on our planet.