Crystal begins by looking at the scale of the threat to minority languages. There are debates over the definition of "language" and estimates of the number of languages vary, but a figure somewhere around 6000 is plausible. Perhaps more important is the distribution of speakers, with 4% of languages accounting for 96% of people and 25% having fewer than 1000 speakers. There are different ways of classifying "danger levels", but there is no doubt that a large number of languages face extinction in the immediate future, while in the longer-term even quite widely spoken languages may be in danger.
Why should we care about language death? Crystal presents five arguments: from the general value of diversity, from the value of languages as expressions of identity, as repositories of history, as part of the sum of human knowledge, and as interesting subjects in their own right. None of these are likely to convince either aggressive monolingualists or the apathetic, but Crystal includes some thought-provoking details and quotes.
How do languages die? Obviously a language dies if all of its speakers die as the result of genocide or natural disasters, or are scattered in such a way as to break up the language community. More commonly languages die through cultural change and language replacement, by assimilation to a "dominant" culture and language. This process is broad and complex, but one major factor is negative attitudes to a language, both in government policy and local communities.
What can be done about this? Crystal looks first at general needs: gathering information, raising awareness (both in local communities and in the international community), and fostering positive community attitudes (sometimes people don't want to save their own language). Any approach must promote the authenticity of the whole community (accepting change and recognising all dialects) and consider language as part of broader culture.
Crystal suggests six key themes in language revitalization: increasing the prestige, wealth, and power of language speakers; giving the language a strong presence in the education system; giving the language a written form and encouraging literacy; and access to electronic technology (the latter being more of a "possibility" than a reality in most cases). He also argues for a stronger emphasis on descriptive linguistics and fieldwork, and stresses the need to build a rounded "revitalization team", involving a broad range of community leaders, teachers, and other specialists as well as linguists.