This chapter analyses the rise, the consolidation and the internal functioning of the MAS-IPSP – a clear instance of movement-based populism – through the lens provided by the theoretical framework described in Chapter 2. The chapter starts with analysing the causally relevant ‘critical antecedents’: the adoption of neoliberal ideologies and practices by all the Bolivian mainstream parties in the pre-crisis era, and the inability of Bolivian syndicalism to act as a leading actor in the long and violent protest cycle triggered by the crisis and popular discontent. Then the chapter focuses on the impressive capacity of alliance building by peasant and indigenist social movements, which animated the protests against neoliberal governments and developed their own ‘electoral arm’ to reach the power. MAS-IPSP’s origins, organisation and early strategies are then discussed, as well as its governmental experience. The analysis of the latter shows how underground tensions within the movements’ coalition finally emerged, thus triggering several ‘inter-organisational struggles’ typical of participative-mobilising populisms, as well as how the movements gradually lost their autonomy vis-à-vis the partisan and governmental elites. Then, a quantitative analysis based on survey data describes the sociological characteristics of the masistas voters and highlights the ‘plebeian’ features of the core-constituencies of the MAS-IPSP. A brief concluding section summarises the findings.