The book provides a theoretical framework to account for the variety of political realignments within the national Lefts, in a delimited set of South American and Southern European countries, in the aftermath of a crisis of the neoliberal model. The argument focuses on the complex interplay between the political-electoral arena, the social mobilisations against austerity and the union movements in order to explain the different paths followed by the national Lefts in the countries analysed and the different kinds of anti-neoliberal populisms that emerged. This chapter discusses in particular why populism, in its anti-neoliberal form(s), proved to be a successful political project during contentious times in highly fragmented, impoverished and mobilised societies, and places anti-neoliberal populism within a broader historical perspective. The last section presents the plan of the rest of the book.