The present paper examines Dutch-French language choice in the history of the Northern Low Countries, focussing on the private domain in the nineteenth century. Seeking to assess the phenomenon from a quantitative perspective, while meaningfully integrating the role of intra-writer variation, we present two complementary approaches. On the basis of a substantial dataset of private family correspondence, we first illustrate a quantitative methodology that allows us to systematically study the sociolinguistics dynamics that determine language choice. The variables under investigation include gender constellations and familial relationships. Secondly, we zoom in on intra-writer variation in three selected family archives, taking a more qualitative perspective in order to add valuable nuances to the ‘bigger picture’.