This book is about the theory and practice of assistance to speech-communities whose native languages are threatened because their intergenerational continuity is proceeding negatively, with fewer and fewer speakers (or readers, writers and even understanders) every generation. In the main, this book is about why most efforts to reverse language shift are only indifferently successful at best, and outright failures or even contra-indicated and harmful undertakings at worst. It attempts to diagnose such difficulties and to prescribe ameliorative and restorative efforts in a sociolinguistically informed way. It draws upon the experience of past and current practitioners of language restoration, it reviews pertinent sociolinguistic research and theory, it examines a fairly large number of cases of attempted reversals of language shift on several continents, and it seeks to suggest a more rational, systematic approach to what has often hitherto been a primarily emotion-laden, "let's try everything we possibly can and perhaps something will work", type of dedication.