One of the most common phenomena of language use among bilingual speakers is language alternation. Yet, from a theoretical perspective, it is impossible in principle both grammatically and socio-functionally. Therefore, a crucial question is how to account for its actual possibility despite this theoretical impossibility. Drawing on Ethnomethodology, this problem is described as that of order in talk in two languages. The book offers a critical reading of current approaches to language alternation as accounts of this essential problem of order.