Background: While farming in France and generally in Europe is continuing to intensify, at the expense of its environmental sustainability, promising alternatives are emerging. Objective: The processes whereby farmers change and transform their own work, to shift from an intensive mode of production to a self-sufficient and autonomous one, need to be formalized if we are to further our understanding of why and how these forms of sustainable farming activity emerge. Methods: We use the development of professional worlds theory, a systemic representation of workers' activity, whereby their experience is formalized. This can be explained as the praxis1, conceptual and axiological underpinnings form a system with the object of the action. The development of a professional world is analyzed according to the evolution of its components and the search for pragmatic coherence within it. We analyzed professional transitions towards self-sufficient and autonomous mixed farming through a case study. Results: Our findings showed that the transition is initiated by the discovery of the unthinkable, awareness of a discrepancy between what the farmers think and what they do, the appearance of problems, and the response to external constraints. Professional transition is a non-teleological and non-incremental process; it corresponds to a comparison with reality, and a resolution of difficulties. This process is stimulated by the use of artifacts instrumented by the farmers. Conclusion: New perspectives are opened up by this formalization of transitions, in terms of (i) support towards sustainable farming and (ii) the design of sustainable farming systems.