The issue of immigration has thus far been conceptualised almost exclusively as a catalyst for radical forms of behaviour. Scholars of political behaviour have focused on the exceptional character of the radical voter, the pivotal role played by radical right parties in explaining the strategies of mainstream parties, and the prevalence of negative attitudes. The aim of this study is to transcend the analysis of a minority of the political spectrum, present only in a limited number of political systems, and instead to comparatively observe the impact of attitudes towards immigration on mainstream electoral competition in Europe on the basis of individual, party and system levels of variation. The thesis has three main findings. First, the issue of immigration has strong potential to affect mainstream voting in contemporary European political systems. Contrary to what is usually implied by the literature on the radical right, attitudes towards immigration have a stronger tendency to generate centripetal rather than centrifugal electoral dynamics. Second, the immigration issue can reshape the morphology of established party systems through two distinct mechanisms of electoral change. The first mechanism is through the mobilisation of existing party supporters, which takes place through voters' calculations of electoral utility in a refined attitudinal continuum, taking into account voters' own positions and those of the parties. Thus, from a spatial voting perspective, the immigration issue can only mobilise parties' core supporters, but cannot easily generate vote transfers between parties. The second mechanism operates in reverse, through acquiring non-identified voters through valence mechanisms of voting. Changes in established electoral boundaries can only take place through voters who are not currently attached to a party, and who are able to link their concern about immigration to parties' competence in dealing with the issue. Finally, the third main finding of the thesis is that not all attitudinal constructs have a behavioural effect. Coherent perceptions constrained by previous left-right individual political predispositions are more likely to have an influence. These perceptions tend to focus on immigrant's adaptability to and compatibility with the host country. By contrast, perceptions framed in terms of superiority or inferiority of immigration vis-à-vis the host society are less likely to be translated into electoral outcomes.