This is the fourth volume in a ground-breaking series of studies on the social history of the Welsh language. The 1891 census was the first to collect information about the language spoken by the people of Wales. It is, therefore, a particularly rich and reliable source for historians analysing the socio-economic structure of Welsh- and English-language ability and the process of language change in Wales at the end of the nineteenth century. In The Welsh Language and the 1891 Census , a detailed analysis of the linguistic evidence provided by the enumerators’ returns is undertaken for the first time. The study concentrates on twenty communities, chosen for their geographical, economic and linguistic characteristics. For each of the selected areas, a detailed picture of the socio-economic pattern of language use has been constructed by examining a range of social variables, such as age, sex, relation to head of household, place of birth and occupation, in relation to the language spoken. Intergenerational language shift, the linguistic influence of extra-family members, and the effects of mixed marriages on language change are investigated, and particular attention is given to migration streams and the presence of incoming strangers and returning kin. The study thus sheds light on the way in which English penetrated traditionally Welsh areas of interest and is certain to provide a sound foundation for further socio-linguistic studies.