How to identify and assess the social and political impacts of a social movement such as the 15M/Indignados in Spain? A particular challenge comes up, first, when its limits and identity are blurred so here we distinguish three types of movement goals and explain how they emerged. Secondly, in order to evaluate their achievements we pay special attention to the usually neglected dimensions of movements’ impacts – their self-reproduction, the non-institutional effects and the ‘unintended consequences’. We argue that the 15M was able to challenge the authorities over the first three years of its existence by creating a counter-hegemonic political culture as well as a manifold set of practical initiatives of self-organisation. However, the institutional impacts were very limited, in spite of some significant successes and side-effects in the electoral arena. This is mainly explained by the resilient cohesion of the power elites and the continuation of the prevailing socio-economic structures.