This book addresses the dialectical evolution of outsider-left parties and movement organizations in the aftermath of mass anti-neoliberal protests. A novel framework and typology for analysing the emergence, development and longer-term legacies of party-building in Bolivia (MAS), Greece (SYRIZA), Spain (Podemos), and Venezuela (PSUV) is advanced. The book evaluates why outsiders transform programmatic promises as they seek office and asks if and how movement organizations challenge “their” party in such scenarios. Case studies highlight that the form of critique from below influences how party leadership respond, in turn shaping whether popular organizations retain support for the party, sponsor alternative parties, or withdraw from institutional politics altogether.