What is French and how has it changed over time? Can we distinguish language history from historical linguistics, and language change from linguistic change? These questions are explored using copious material from the history of the French language, concentrating on changes in the relatively modern period in particular. Posner explains how change comes about and how changes at different levels of language interact, and the role of sociological and ideological factors is set against the internal mechanisms that trigger change. This work makes a substantial contribution to the theory of linguistic change, as well as to discussion of the relationship between language and history in French-speaking areas, including Canada and French Creole-speaking countries.