This chapter reflects the content of a series of lectures at the Graduate School Subject Specific Learning and Interaction in Elementary School (INTERFACH, 5–8 July 2022, Halle). It focuses on the emergence of comparative research in Didactics in the French-speaking context. The aim is to introduce the main concepts of the Joint Action framework in Didactics ( JAD) and to explain how they are used within the Research Group in Comparative Didactics1, at the University of Geneva. To do so, I use a series of empirical examples that I analyze from several perspectives, each of which is complementary to others. In the last part of the paper, I show the importance of the analyses carried out using this framework for understanding issues about the didactic transposition in the formation of science as a school subject.