This paper discusses the consequences of language shift through erosion on the basis of an analysis of the development of the situation in French Flanders. This part of northern France used to be part of Dutch-speaking Flanders until 1678, when it was annexed by the French crown. Although the language shift process started almost immediately it only gained momentum after the French Revolution, as a consequence of a deliberate Frenchification policy and legislation on the part of the French authorities. Recent inquiries and research reveal that we are currently witnessing the ultimate stages of language loss, preceding the complete extinction of Dutch as a native language in France. The final part of the paper attempts to sketch the theoretical language-incontact framework, breaking down the chronological evolution into diglossic, bilingual and (almost) monolingual phases, taking into account the geographic, social and functional variables by which language shift and loss is characterised.