In the last thirty years, alternation in government has become a common practice in Western Europe. Unfortunately, democratic theories and theorists have hitherto mostly neglected or taken for granted this crucial phenomenon in many political systems. This thesis aims to fill this gap between theory and practice. In the first part, the dissertation puts forward a new and original conceptual toolkit for the analysis of government alternation across countries and through time. Three dimensions, or faces, of the concept of alternation (i.e. actuality, possibility and probability) are singled out, defined and thoroughly operationalised. This process of concept reconstruction makes it possible to paint a large historical fresco of the development of government alternation in Western Europe throughout the whole post-war period. The second part of the thesis is devoted to the empirical analysis of the suggested determinants of alternation in government. All the factors that may have an impact on the occurrence of alternation in its manifold manifestations are scrutinised and correlated to the diverse ways in which West European party systems change their cabinets across space and time. Furthermore, the analysis carried out in this part of the thesis directly challenges much of the conventional wisdom that has accompanied the study of alternation since its uncertain inception. More precisely, the results of the bivariate analyses show that the occurrence of alternation is not strictly correlated with the fragmentation of the party systems or the proportionality of the electoral systems. Other factors, such as the existence (and the strength) of anti-system parties, the role of pivotal actors, voters’ availability to change their electoral behaviour or the cabinet size, contribute to the explanation of the emergence and the persistence of a pattern of alternation in government. In the last part of the thesis, I carried out a comparative time-series cross-section analysis of the determinants of government alternation in seventeen West European countries. Partially, this set of multivariate analyses confirms some of the evidence collected in the previous section. However, and in addition to that, the large-N statistical analysis demonstrates that different explanatory factors account for the variation in the three dimensions of alternation suggested above. Moreover, the same argument holds true for the explanation of the development of government alternation, in particular its accelerated rise since the 1980s. Finally, in the concluding chapter I analyse, firstly, the foreseeable evolution of government alternation in Western Europe, especially in relation to the impact of the current economic crisis on the functioning of West European democracies. Secondly, the chapter closes with the suggestion of a new typology of party systems based on the existence of a bipolar pattern of inter-party competition and the possibility of a wholesale replacement of the governing parties.