Since the turn of the Century, social protection has expanded rapidly across the Global South. The pace by which these programmes have expanded, and the type of programmes that have been adopted, vary substantially across countries. This article has two objectives: first, it provides an overview of the political economy literature of social protection adoption, focusing on the factors that the literature highlights as underpinning the adoption of social protection programmes in MICs and LICs. Second, we empirically examine these underlying determinants. Overall, we find evidence indicating that past democratization has had a positive effect on the current expansion social transfers. Electoral democracies seem to have favoured the expansion of CCTs and social pensions, whereas autocracies and infant electoral democracies have favoured pure cash transfers and public works, which are, on average, smaller in scale and are more prone to political clientelism. The level of economic development, demographic characteristics and state capabilities also matter for the adoption and scalability of social transfers.