Saussure, the founder of General Linguistics, was primarily a historical linguist, and knew very well the methods of the Indo-European reconstruction, which is based on the knowledge of ancient languages. My work has the aim of showing Saussure’s passage from Indo-European studies to the theoretical study of la langue, and especially to highlight the connection between these two forms of inquiries in the CLG. In order to account for this transition I analyze the editions of Saussure’s three university courses, which are the basis of the CLG, as well as the new manuscripts discovered in 1996. We can see that some parts of the CLG, for example the third one, dedicated to diachronic linguistics, would be unthinkable without Saussure’s solid background in the field of historical-comparative linguistics, and that even the theoretical sections of CLG are explained with examples and arguments that stem from the Indo-Europeanist field.