Bilingual dictionaries from the 17th and 18th centuries – particularly those in the tradition of Antoine Oudin’s Recherches – supply us with valuable information on language description, on its use, and on linguistic conceptions at crucial moments in the histories of the two national languages compared here: Italian and French. The contribution of these dictionaries is just as vital in the area of French and Italian cultural history with regard to the social and historical conditions that justified their creation and the cultural relations that can be established – on both the diachronic and the diatopic axes – between two linguistic communities. Bilingual dictionaries take on, moreover, a multifaceted significance: for the comparative lexicographic methodology in place during this period; for the linguistic and extralinguistic content of the lemmas and accepted locutions that aimed to teach linguistic and cultural competence; for the value of documenting illustrated linguistic phenomena and lexical units strongly linked to identity; and for the focus on semantic and cultural divergences in the transition from one language to the other.