Actions of political party elites are central to many theories of new issue alignment in mass electorates. But these theories seemingly have little to say about the mass party implications of the most important recent development in American party politics: elite party polarization along the existing dimension of conflict over the scope of the federal government and its role in providing social services. This project addresses the impact of elite polarization on mass party change in the United States, paying particular attention to how changes in the political context affect the decision-making processes of individual citizens. Chapter 1 develops an equilibrium theory of mass-elite linkages, showing that mass parties have polarized on the existing dimension and that mass and elite polarization are linked in a systematic way. Chapter 2 explores the impact of this mass polarization for changes in the relative size of party coalitions. The chapter develops a theory of macro-micro linkages in the party system, explaining how macro-context and individual-level behavior interact to produce aggregate-level change. The analysis shows that the Democratic Party has become smaller not because of a decline in the importance of social class or the growing prominence of "cultural" concerns, but rather because polarization-and the resultant clarity of elite positions-has caused many citizens with conservative scope-of-government preferences to become Republicans. Chapter 3 addresses the impact of polarization on electoral decision-making, exploring the relationship between partisanship-policy preference consistency and the decision to cast a party-line vote. I find that, dependent on certain attributes of the individual and context, individuals whose policy preferences are broadly consistent with those of their party's elites are more likely to vote for candidates of their party. Recent increases in the number of "consistent" citizens, brought about in large part by elite polarization, explain the resurgence of party voting in the electorate. Taken together, these chapters suggest that scope-of-government issues play a larger role than any time in recent history in defining the mass party system. They also provide a framework for thinking about the dynamic relationships between context, citizens, and political outcomes.