Chinese have been immigrating to Siam for at least six centuries. We are concerned here with the process whereby the descendants of Chinese immigrants become full members of Thai society. Assimilation is, of course, a social process. For the descendants of a given immigrant, its progress is defined by increasing social intercourse with members of Thai society, first public and then private and intimate; and by self-identification in an ever larger proportion of social situations as Thai rather than Chinese. Since social interaction is based on linguistic communication, assimilation perforce involves a command of the Thai language. Taking over the language of the society with which immigrants are in contact is but one part of acculturation, that is, the progressive incorporation of the way of life of the other society. While extensive acculturation can take place without complete assimilation, complete assimilation is inevitably accompanied or closely followed by fairly full acculturation. For our purposes here, assimilation is considered complete when the immigrant's descendant identifies himself in almost all social situations as a Thai, speaks the Thai language habitually and with native fluency, and interacts by choice with Thai more often than with Chinese.