This study reveals the processes of language erosion and maintenance as they are affected by ethnicity and ethnic group interaction based on a 1976 survey of two communities in Wales, one largely anglicized and the other largely Welsh-speaking. Following a brief description of basic linguistic ability (speaking and reading) in the two communities, a detailed account of the variation of linguistic usage within contexts or domains is presented. Attitudes toward language retention and the perception of linguistic decline are examined in terms of the respondents' age, length of residence, occupation, and Welsh-speaking ability. The subjective aspects of ethnic identification in these groups are explored, including the relationship of the respondents' stated nationality to their place of birth, length of residence, ability to speak Welsh, religious denomination, age, and occupation. Conclusions regarding ethnic identity and language maintenance in these communities to date and in the future are outlined. (MSE)