The Chilean urban poor led crucial mobilisation throughout most of the 20th century. Scholars argue that different factors explain the demobilisation of that sector during the democratic transition (the early 1990s). Through an ethnographic comparative approach, this thesis compares two neighbourhoods. Their similitudes cannot explain why while one of them sustained contentious collective action in time, the other became demobilised as most other neighbourhoods. As in many other studies, what explains the survival of contentious collective action is a mobilisational identity. This research moves beyond those accounts to explain why mobilisational citizenship emerges in some communities and not in others. The interaction between four dimensions explains mobilisational citizenship: agentic memory, belonging, boundaries, and decentralised leadership. The sustainability of mobilisational citizenship depends on grassroots activists' capacity to transmit collective identity as political capital. The Chilean case shows that autonomy is crucial for mobilisational citizenship. In cases in which political parties establish networks of loyalty and clientelism promoting the monopoly of political capital at the grassroots level, communities cannot develop and sustain a mobilisational identity.