For years, the prevailing opinion among academics has been that language is embedded in our genes, existing as an innate and instinctual part of us. In this bold and provocative study, linguist Daniel Everett argues that, like other tools, language was invented by humans and can be reinvented or lost. He shows how the evolution of different language forms--that is, different grammar--reflects how language is influenced by human societies and experiences, and how it expresses their great variety. Combining anthropology, primatology, computer science, philosophy, linguistics, psychology, and his own pioneering research with the Amazonian Pirahã, and using insights from many different languages and cultures, Everett presents an unprecedented elucidation of this society-defined nature of language. In doing so, he also gives us a new understanding of how we think and who we are.