During the 20th century there has been a widespread pattern of language shift among the indigenous communities of the United States and Canada. The language-of-work hypothesis posits that if the national language is used as the language of work for virtually all jobs in a minority-language community, the national language will, within a few generations, replace the minority language as language of the home as well. This language shift involves a series of steps: (1) indigenous language groups moving from kinship-based economies to wage-based economies; (2) a significant portion of community members using a language other than their mother tongue in the workplace; (3) a change in views as to what language skills children will need to prepare for the future; and (4) parents making the national language the language of their children. Other factors promoting language shift may include improved transportation and communication, government policy, intercultural marriages, etiquette, and intolerance. Language shift retardants may include religious use of the minority language, population size, linguistic similarity, and viability of traditional means of earning a living. Related theories for language shift are discussed with emphasis on their ties with the language-of-work hypothesis. Two appendices describe application of the hypothesis in three types of language-based work environments. Contains 44 references. (SAS)