This book explores partisan dealignment in France between 1978 and 2012, with a particular focus on the blue-collar electorate and its relationship with the political parties of the established left (the Socialist Party, or Parti socialiste , and the Communist Party, or Parti communiste français ). It highlights the distinctiveness of blue-collar partisanship in a context of significant political, social and economic change and compares it with patterns of partisanship in the wider electorate. The voter-party relationship is self-evidently a bilateral one which can be modified both on the demand side, because voters change, and on the supply side, because parties change. Four factors are identified as playing a key role in partisan dealignment: value change, policy convergence, political sophistication and political trust. There is compelling evidence that while each of these makes a contribution, it is changes in the behaviour of the parties that are driving partisan dealignment among blue-collar workers in France.