What social groups support which political party, and how that support has changed over time, are central questions in the sociology of political behaviour. This study provides the first systematic book-length reassessment and restatement of the sociological approach to American politics inmore than 20 years. It challenges widespread arguments that the importance of social cleavages have declined precipitously in recent years in the face of post-industrial social and economic changes. The book reconceptualizes the concept of social cleavages and focus on four major cleavages in American society: class, religion, gender, and race, arguing a that a number of important changes in the alignments of the groups making up these four cleavages have occurred. The book examines the implications of these changes for the Democratic and Republican Parties. The findings of the book are examined in light of the central dilemmas facing the two major parties in the contemporary political environment.