In the past twenty years, extreme parties have emerged and strengthened across European party systems, such as Podemos in Spain, the Afd in Germany, or Fratelli d’Italia in Italy. Could the polarization of parties be the cure to growing abstention in European systems by offering true political alternatives to disengaged citizens? Or, alternatively, is increasing partisan divisions becoming major threat to the working of our democracies? This thesis tackles this question with important normative implications by determining whether and how party polarization in European multiparty systems enhances electoral mobilization. Using a novel mixed-method and abductive approach, this dissertation’s main contribution is to uncover the role of fear and indifference as political reactions to party polarization. This thesis follows a three-step design that combines a cross-sectional times series analysis in 21 European countries, a comparative qualitative focus group analysis in France in Belgium, and a Survey Experiment fielded in France. First, this analysis provides evidence that party polarization may mobilize some voters when parties become increasingly divided on cultural issues. However, qualitative findings show that this may have less to do with the broadening of political alternatives than the role of parties in triggering strong negative emotions and a sense of fear, anxiety, and threat related to these issues. Second, while much of the literature warns us about the threat represented by rising affective polarization and the disproportionate mobilization of the most partisan, results suggest instead that party polarization may enhance widespread indifference toward parties, which may be at least as harmful for participation and the working of our representative democracies. Overall, this dissertation contributes to the growing literature on the consequences of party polarization and partisan divisions by highlighting promising theoretical avenues going beyond the study of the most partisans.