“On 4 November 1995 Kasabe existed; on 5 November it did not.” This briefobituary in David Crystal's book (p. 1) does not refer to a creature. It refers to an Africanlanguage, known as Luo, that had been spoken in Cameroon; on the day in question, Bogon, thelast speaker of Kasabe, died, taking his language with him. According to Crystal, half of theworld's current languages are in danger of dying, and the situation is so grave that aninternational and interdisciplinary effort must be mounted to rescue them. Crystal has written thisbook to alert us to the peril and to suggest ways in which our linguistic diversity might bemaintained.