Résumé : The purpose of our paper is to propose a definition of progress based on the relationship between economic development and civil development, according to the lesson of Classical authors, especially Adam Smith. Firstly, we analyze the interaction between economic development and civil development, in a circular cumulative causation, and the various causal relationships between these two elements. Secondly, we propose a synthetic index of progress, which on the one hand takes account of the different components of development (social, civil, economic and ecological) and on the other hand is based on the concept of ‘social sustainability’ of progress, defined as balanced improvement of all its dimensions.