Scholars have long debated the individual-level relationship between partisanship and policy preferences. We argue that partisanship and issue attitudes cause changes in each other, but the pattern of influence varies systematically. Issue-based change in party identification should occur among individuals who are aware of party differences on an issue and find that issue to be salient. Individuals who are aware of party differences, but do not attach importance to the issue, should evidence party-based issue change. Those lacking awareness of party differences on an issue should show neither effect. We test our account by examining individuals' party identifications and their attitudes on abortion, government spending and provision of services, and government help for African Americans using the 1992-94-96 National Election Study panel study, finding strong support for our argument. We discuss the implications of our findings both for the microlevel study of party identification and the macrolevel analysis of partisan change.