From a broad review of the literature and empirical studies conducted in Latin America and in France, we consolidate the concept of activity system applied to family farming. This concept brings together fundamental works of various disciplines on the notions of activity, work, knowledge, resources, decision-making and rationality, dynamic of systems, innovation and development. This analytical framework imposes to define the activity system components (social entity, activity, motivation and resources) and its environment. The study of the interactions and of the dynamics, especially in its historical dimension, is intrinsic to the activity system approach. The activity system thus defined invites to a comparative approach. It allows to categorize social and technical forms observed in the various expressions of rural life, and not only the agricultural ones. It leads to re-examine the analysis of the activity, practices and decisions in a system where interact activities, resources for action and decision, the representations and the multiple motivations of the actor. It allows revisiting the way the activity systems are connected with higher levels of organization, be it markets, territories, social organizations or public policies.