Based on two studies, our objective is to promote an approach to professionalization in terms of activity. The first study analyzes, via a biographical approach, the dynamics of transformation linked to entry into the commercial professions of an automotive subsidiary. The second study focuses on the acquisition of formalized know-how by agricultural trainers through a support system, via a clinical approach to the activity. Aimed extensively or intensively, this way of apprehending professionalization is variable. By combining the results of the studies, professionalization appears to be centered on the experience and autonomy of the individuals, who develop their own goals and above all engage in socio-reflective acts. Finally, such an analysis can produce effects on professionalization and on work.