This chapter presents an overview of language death, dormancy, and revival in the Catalogue of Endangered Languages. It also presents the Catalogue's terminology and policies regarding languages with no native speakers. The chapter discusses what is known about language death in the past, as compared with language loss in decades, finding that languages are now being lost at rates unparalleled in known history. Languages cease to be spoken for a wide variety of reasons, and under a wide variety of circumstances. Languages have come into existence, been transmitted for a time, and disappeared since humans have been talking; they have always given way to other languages as a result of social, environmental, economic, political, and other pressures. Language revitalization movements around the world are growing, and there already exist success stories that demonstrate the possibility of maintaining currently viable languages, of revitalizing endangered languages, and even of reviving formerly dormant languages.