The purpose of this dissertation is to analyse the hybrid composition of a social movement from the study of its activist cultures in the making of a great mobilization. As a study case, I take the Chilean social movement against the retirement pension fund system (No más Afp) whose public exposure took to the streets as the result of two forms of activism. The movement aspires to end with a system based on individual capitalisation and replace it with a solidary form of pension profit sharing. I argue that the public uprise of the No más Afp movement is the result of the encounter of two activist cultures: (1) the union-movementist activist culture, and (2) the indignant activist culture. Both function as specific forms of being and doing activism under the logic of organisation, the construction of reasons and criteria to rebel, and their relation with politics and activist's commitment. Both will end up facing each other, with different levels of management of their tensions, acknowledging their contribution to the movement.