In this chapter we ask two questions: First, we ask whether these governments, exemplifying best-case scenarios in Latin America, have embarked on a viable path toward a sustainable social democratic welfare state. Second, we ask whether and why they differ in their approaches and progress on this path, paying close attention to how the parties\u27 organizational characteristics influence this variation. In their introduction, Levitsky and Roberts classify the left parties in Chile and Uruguay as an institutionalized partisan Left, distinguished between an electoral-professional Left and a mass-organic Left. Uruguay\u27s FA is an example of a mass-organic left party, while Chile\u27s PS is an example of an electoral-professional left party. We contend that this difference in organizational character has important consequences for the types of social policy reform adopted