SOMBRERO aims at studying the biographical consequences of participation into social movements. It is from the angle of how trajectories are formed that we propose to broach this question and to determine what involvement leads to rather than, more conventionally, what produces involvement. Thus, it is a matter of understanding how participation is likely to have a continual influence, through redefining or modifying individual behavior and perceptions. Beyond the explicit learning dispensed by activist organizations, or the socializing effects of exposure to political events, it is a matter of studying the ways in which political commitment affects all individual behavior and perceptions, in other words of considering that all participation, however sustained or intense, has secondary socializing effects. For this, we have recourse to a process and multi level approach of activist trajectories, based on an interactionist and configurational approach of life-course, what we call a sociology of « Activist careers.» We start by identifying individuals who were activists in the 1970s (from immediately after 1968 up to 1981) in three “movement families” (the feminist movement, workers’ unions and extreme-leftist organizations) and in five urban locations (Marseille, Lyon, Lille, Rennes, Nantes). On one hand, we produce a mapping of the 1970’s multi organizational fields in each city under study; on the other hand we conduct 500 life-histories, associated to a “sequence analysis” of life calendars. Such a research design will allow us to reconstruct these people’s life course in order to articulate micro (idiosyncrasies) meso (secondary socialization through commitment) and macro (local and national contexts) levels of analysis in order to make sense of individual trajectories.