Ramsey begins with the 1913 Conference on Unification of Pronunciation and the history of language reform which produced Putonghua, modern standard Chinese. He explains why, although Chinese dialects are more varied than the Romance family of languages, they are nevertheless considered one language and not several. (Throughout he offers comparisons, analogies, and examples likely to be familiar to English speakers.)
He goes on to describe the geographical and historical differences between northern and southern China. The question here is not why there is more linguistic diversity in the south, but why there is such exceptional uniformity in the north: Ramsey canvasses both ecological (relative ease of communications) and historical (relatively recent movements of people) explanations. The linguistic influence of the north on the south is ongoing: historically the dominant process has been the southward migration of Chinese speakers and the adoption by local populations of Chinese culture and language.
Three chapters describe standard Chinese pronunciation and grammar and the differences between the standard and the major dialects: Mandarin (the basis for the standard language), Wu, Gan, Xiang, Yue (Cantonese), Min, and Hakka. This material is fairly dense, going into details of sound systems, morphology, and syntax, but it is comprehensible without any knowledge of Chinese languages (though some basic general linguistics is assumed, here and elsewhere). Ramsey also finds space to debunk traditional claims that Chinese is inferior to Indo-European languages because of its grammatical structure. Then there are chapters on the history of Chinese, focusing on the reconstruction of Middle Chinese, and on its modern writing system and the debate over simplified characters and Pinyin Romanization.
The second half of The Languages of China covers the minority (non-Han) languages spoken within the borders of China. Ramsey begins with the history of Chinese policy towards minorities and the study of their languages. Language has played an unpredictable role in defining minorities: some are clearly distinguishable both culturally and linguistically (the Uighur, for example); others are culturally hard to distinguish from their Han neighbours (the Zhuang); and some speak Chinese dialects and are distinguished only by religion or culture (the Muslim Hui).
Two chapters survey the minority languages systematically: in the north the Altaic language family (Turkic, Mongolian, and Tungus); in the south a broad "linguistic area" (with shared features resulting from diffusion) containing representatives of several language families (Tibeto-Burman, Tai, Miao-Yao, Mon-Khmer) and many unclassified languages. Strangely, Tibetan itself is not covered, on the grounds that Tibet forms a linguistic area all of its own.
Especially with the more significant languages, Ramsey goes into considerable technical detail about sound systems, syntax, grammar, and scripts where they exist(ed). For example, of Zhuang we read
Standard Zhuang has eighteen consonants. In Wuming the phonemes b and d are pronounced [qb] and [qd]; in some other localities the glottalization also appears before m and n in initial position. The consonant v patterns as a semi-vowel ...and so on. But the ten pages on Zhuang offer a lot more. Among other things, we learn how the Guangxi Zhuang Autonomous Region was created in 1958, even though the minority of the population that spoke Zhuang were bilingual and happy to be considered Han: it was government policy, stressing past mistreatment, to revive minorities and their languages.
Non-specialists without an interest in the linguistic details will still appreciate Ramsey's lively survey of China's languages.