We estimate the causal effect of the number of candidates on turnout in applying a regression discontinuity design (RDD) to data from 13,974 legislative and cantonal electoral districts in France since 1978. In the two-round system used in these elections, the candidates who pass a certain vote threshold in the first round can participate in the second round. We use this discontinuity in qualifying to compare districts in which the third candidate falls just above and below this threshold. We find that an additional candidate increases turnout by 4.1% points and the share of valid votes by 7.7% points. Further, we look into the mechanism and find evidence supporting the alienation theory, according to which turnout increases the most when the third candidate is from a different ideology than the two first. We also confirm this finding with an analysis of individual-level survey data from the 2012 legislative election.