This chapter explores the adoption of mobilization strategies in the case of the MAS in Bolivia. Drawing on extensive interviews with representatives of the party and societal organizations, as well as archival materials and ethnographic work in local organizations, it shows how the shared experience of moments of solidarity between the party proto-leaders and organizational allies during the party’s founding moments determined whether party–organization ties would later become institutionalized by adopting routinized rules and mechanisms that governed how candidates would be selected and factional disagreements would be settled. As it documents across different organizational allies of the party, where the party’s tie with an organization became institutionalized, these rules and mechanisms ensured that the party could rely on organizationally mediated strategies.