This book is the first full evaluation of the Proto-Australian hypothesis, which proposes that most Australian languages have a common ancestor: Proto-Australian [PA]. Using the standard methodologies of historical linguistics, the authors show that nearly all Australian languages descend from PA. Given that PA was a single language, it was spoken only in a small area of Australia. Its descendants have spread across the continent. Current theories of language spread do not offer clear motivations for large-scale spread in hunter-gatherer economies. This raises significant questions for analyses of Australian prehistory and archaeology specifically, and more widely for general theories of hunter-gatherer prehistory and language spread.