Televised debates are now an expected component of the American presidential election campaign. A meta-analysis was used to cumulate the research on the effects of watching presidential debates. General campaign debates increase issue knowledge and issue salience (the number of issues a voter uses to evaluate candidates) and can change preference for candidates' issue stands. Debates can have an agenda-setting effect. Debates can alter perceptions of the candidates' personality, but they do not exert a significant effect on perceptions of the candidates' competence (leadership ability). Debates can affect vote preference. Primary debates increase issue knowledge, influence perceptions of candidates' character, and can alter voter preferences (the effect sizes for these variables are larger in primary than general debates). The effect sizes for the dependent variables with significant effects were heterogeneous (except for effects of debates other than the first on vote preference). No support was found for several possible moderator variables on issue knowledge, character perceptions, candidate competence, and vote preference: nature of subject pool (students, nonstudents), study design (pretest/posttest, viewers/nonviewers), number of days between debate and election, or data collection method (public opinion poll or experimenter data). The first debate in a series had a larger effect on vote preference than other debates, but was not a moderator for other dependent variables. The possibility that other moderator variables are at work cannot be rejected.