This book presents the main results of an electoral panel study which is both unique and innovative not only in French political research but also among Western European electoral studies. The survey was conducted among a sample of 1,846 French voters interviewed on four separate occasions (2007 Presidential and Legislative elections). Electoral trajectories can thus be observed revealing the main trends in electoral behaviour and voting patterns across the electorate. The analysis of such trajectories and patterns mobilizes not only the usual explanatory factors (demographics, political leanings and identifications) but also another set of political variables (issues, the campaign and the media, the candidates' image, how electoral decisions are made, hesitation in voting intentions). This study also provides interesting findings on electoral volatility, including abstention.