| How do constituents hold their representatives accountable? This dissertation examines three elements of voter behavior that constitute the foundations of accountability: the preferences they have over the policies politicians vote on, the knowledge they have of their representatives' records, and the sanctions they levy in response.;Using a battery of new survey questions I designed and wrote for the 2006 Cooperative Congressional Elections Study, the first half of the dissertation explores the ways individual constituents help keep legislators dedicated to public opinion. Most voters have preferences over the policies their U.S. senators discuss. They also hold beliefs about how their legislators have voted on these policies, although these perceptions can be systematically biased by the party labels incumbents wear. Finally, these perceptions of how well represented they have been strongly influence constituents' vote choice. In contrast to theories of retrospective voting, which argue that voters are swayed by policy outcomes such as the strength of the economy and military affairs, I show that constituents respond far more strongly to the policy positions the incumbent has taken.;The second half of the dissertation demonstrates that this individual-level behavior can be powerfully shaped by the political conditions under which constituents make their decisions. Electoral competition, the diversity of the constituency, and descriptive representation each alter the extent to which incumbents are held accountable. In some contexts, voters know a great deal about what their legislators have done; in others, knowledge of the incumbent's record is scarce. In some places, constituents' evaluations of their senators are almost completely determined by the positions they take in office; in others, policy congruence fades in importance and the incumbent's record has little effect on her electoral fortunes. In contrast, one of the most-discussed findings from the congressional literature---the electoral advantage legislators gain from long-term incumbency---has no impact on the way voters hold them accountable. |