Introduction - organization and collective action. Part 1 Dismantling the idea of organization: affectivity and calculus - the relativization of rationality; from instrumental organization to organized anarchies - questioning organization cohesion; the organization and its environment - fuzzy organizational borders. Part 2 From organization to organized action: the structuration of contexts of action - interdependence, negotiated exchange and the sustainability of actors; the mixed regulation of field of action - the notion of a concrete system of action; local orders and social regulation. Part 3 The organizational approach to collective action - elements of a mode of reasoning: actors and their rationality; the contingency of actors - the notion of system; power as capacity for action. Part 4 The organizational approach as a tool - implications for research and action: the construction of a grounded theory - induction and pragmatic value in analyses; the importance of the strategy of change; a cognitive operation - the gamble on knowledge and reasoning. Conclusion - another way of relating theory to practice.