The study provides the first thorough empirical examination of how individuals' knowledge of and opinions about the candidates and issues of a campaign affect participation. The study proposes a campaign attention model in which people assess whether there is someone for whom to vote before deciding whether to vote. More specifically, the model posits three candidate-based conditions for participation: knowledge, distinctiveness, and preference. First, individuals who have knowledge of the candidates or issues are more likely to vote than those who do not. Second, individuals who perceive the candidates as distinct from one another are more likely to vote than others. Third, individuals who judge at least one candidate favorably are more likely to vote than those who do not. The model is tested in previously unstudied Senate elections. The results of a probit analysis for the 1990 midterm Senate races indicate the importance of the campaign attention model. Individuals' issue awareness, issue preferences, candidate recognition, perceived candidate differences, and candidate preferences significantly affect individuals' decisions to go to the polls, controlling for the effects of their demographic characteristics, political involvement, and the electoral context.