Résumé : This PhD thesis focuses on Euroscepticism in Belgium. It presents four studies, each relying on different and partly overlapping strands of the literature on Euroscepticism, public opinion and voting behavior and party competition. Each of these studies contains an empirical analysis, using various quantitative and qualitative research methods. The first study focuses on the relationship between Eurosceptic supply and Eurosceptic demand. It particularly looks at voters whose attitudes combine Euroscepticism with moderate socio-economic views. Confronted with extreme-left and extreme-right Eurosceptic parties (and no such offer at the socio-economic center), they might vote for a party that reflects their Eurosceptic views, but not their socio-economic preferences. The paper identifies such ‘unserved voters’ in the Belgian population, and it tests three hypothetical ways in which they may deal with this dilemma when they vote. The second study builds upon this knowledge and focuses particularly on the act of ‘issue-voting’ in the context of Belgium. The paper shows that even in a context where EU politicization is low, where Eurosceptic parties are particularly extreme in left/right terms and have low electoral viability, voters opt for Eurosceptic parties because of their EU-attitudes. The third and four papers use the multi-level governance context of Belgium to empirically proof the point that Euroscepticism is a specific form of the more general concept of system-opposition. The third paper looks at public opinion toward competence distribution in a multi-level context, and the fourth paper investigates how political parties deal with system-opposition and system-support towards multiple levels: the regional, the federal and the European level.The general conclusions from these four papers are, firstly, that EU politicization can only be fully understood in the specific, national political and institutional context in which it takes place. Secondly, the studies show that a more refined conceptualization and measurement of EU politicization, going beyond binary conflict and Euroscepticism as its primary manifestation brings additional and valuable insights, and should be further developed in the literature.