The Parisian bookstore and publisher Honoré Champion nourished a close relationship with the Institut d’Estudis Catalans and the Biblioteca de Catalunya, two institutions arising in Barcelona in the early twentieth century with the aim of fostering modern research. La Librairie Champion was quick to collaborate actively in disseminating Catalan publications in France, while at the same time supplying bibliography for research conducted in Catalonia. This article examines the correspondence conserved in Barcelona between the Catalan institutional tandem and the French bookstore-publisher with a view to exploring their commercial relations: co-publishing projects, distribution policy, sales dealings, etc. Moreover, the article spotlights in particular the most personal aspects of the relationship: the attitude of Édouard Champion at the head of the business; Catalan researchers and their visits to Paris; relations with other French scholarly institutions, and so on. Finally, we turn to the crisis that confronted the Paris-based publisher and the gradual decline of the relationship.