This dissertation examines how voters make decisions during direct democratic campaigns, focusing on the determinants of vote stability and change. Using panel surveys, experiments, and political advertising data from four ballot campaigns in Switzerland and California, I track voters throughout real-world campaigns to identify when and why opinions change. Drawing on political psychology theories, I investigate how policy information and elite cues shape vote choices, particularly when they conflict; how campaign advertising persuades voters; and how individual characteristics such as attitude strength, partisanship, and political sophistication moderate information processing. The findings reveal that a sizable share of voters change their opinions during campaigns, following predictable psychological patterns. Challenging conventional wisdom about partisan dominance, voters strategically choose which information to rely on based on how strongly they feel about policy issues, demonstrating sophisticated engagement with democratic decision-making.