This project examines ‘left populist’ presidents in Latin America. It asks, ‘Why do some left populist presidents in this region engage in policy switching while others do not?’ Policy switching is where presidents renege on campaign promises in office. Typically, the answer to this question is found in either institutional or economic factors. However, these explanations do not provide a complete account of why some presidents are ‘switchers’ but others are not. Left populist presidents typically front personalistic or poorly organised political parties; they eschew traditional institutional constraints; and they switch even amid favourable economic conditions. This project argues that switching can only be fully understood in the context of pressure exerted by civil society in the region. When the president faces pressure from civil society, switching is less likely to occur. To test this proposition empirically, this project examines four left populist presidents from three Andean nations – Bolivia, Ecuador and Peru – in terms of their general policy promises, as well as specific promises regarding constitutional reform, food sovereignty, and resource extraction policy. There is strong support for the argument. In cases where civil society was not mobilised or lacked articulation, populist presidents were more likely to move away from key promises. In cases where civil society was better articulated and strongly mobilised, however, populists tended to comply with their promises. This project also demonstrates the need to ‘unpack’ switching as typically framed. It is important to distinguish not only between presidents who 'switch' and those who do not, but also between those who keep their promises for a period of time and only then switch, and those who switch on some of their promises but not others. In these ways, this project provides the most detailed study of policy switching by left populist presidents in Latin America to date.