Through analysis of the dynamics of decision-making on migration in Sicily, this EUI working paper written by Andrea Pettrachin within the framework of the MIGPROSP project shows how party elites define strategies to politicise (or not) the migration issue. Conventional explanations of the politicization of immigration have largely neglected decision-making processes and explicitly ignored the reasoning of political actors, assuming that cognitive factors and strategic considerations are less relevant in the migration policy domain than in others. They conversely assume that party elites politicise migration in reaction to pressures caused by increasing flows or issue salience, anti-migrant public attitudes and/or far right propaganda. In contrast, this paper shows how actors’ understandings of migration flows and of public reactions are formed, and how they shape or influence the dynamics of politicisation. By doing so, the paper develops three key arguments. First, it is not self-evident that increases in migration flows, issue salience and/or social mobilisations lead to political contestation of migration or initiate reactive responses by political elites. Second, party elites’ decisions to politicise migration or not are shaped by their understandings of the effects of migration on underlying social systems rather than by objective evidence about public attitudes or social mobilisations. Third, these understandings are embedded in narratives, influenced by inherited traditions, and reinforced by the outputs of the very decision-making dynamics that they contribute to shape. To develop these arguments, the paper adopts an actor-centred constructivist approach and investigates decision-making dynamics by applying insights from framing theories and sensemaking approaches.