Every language in the world shares a few common features: we can ask a question, say something belongs to us, and tell someone what to do. But beyond that, our languages are richly and almost infinitely varied: a French speaker can't conceive of a world that isn't split into un and une, male and female, while Estonians have only one word for both men and women: tema. In Dyirbal, an Australian language, things might be masculine, feminine, neuter - or edible vegetable. Every language tells us something about the people who use it. In I Saw the Dog, linguist Alexandra Aikhenvald takes us from the remote swamplands of Papua New Guinea to the university campuses of North America to illuminate the vital importance of names, the value of being able to say exactly what you mean, what language can tell us about what it means to be human - and what we lose when they disappear forever.