This chapter reviews the main theoretical and empirical contributions to the debate on the politicization of the European Union (EU) by focusing on the role of public opinion in the process of European integration. The era of “permissive consensus” started to vanish in the mid-1980s, and pro-EU political elites are now hampered by a popular “constraining dissensus” that prevents them from making decisions regarding the integration of the Union without considering public opinion. These social transformations have fostered the proliferation of theoretical and empirical works trying to uncover the processes of politicization of the EU and its effects on public opinion. This chapter discusses in detail the main postulates of the postfunctionalist theory and revises the concept of politicization of the EU, its patterns and trends, and its societal implications.