Research on comparative voter turnout has produced a puzzling set of findings: proportional representation (PR) electoral systems increase turnout, but multiparty systems decrease turnout. This paper provides new evidence to resolve these conflicting findings by developing and testing the hypothesis that the presence of a pre-electoral coalition (PEC) increases voter turnout by reducing uncertainty about the possible government that will form after the election. PECs provide credible signals to voters about the commitment of participating parties to govern together, making the election more decisive as a mechanism for selecting the government by clarifying the possible electoral outcomes. This increased electoral decisiveness increases voters' incentives to turn out. This hypothesis is tested on a data set of 223 national legislative elections in 19 parliamentary democracies between 1970 and 2002, with the results indicating that the presence of a PEC increases turnout on average by more than 1.5 percentage points. This finding provides support for the argument that the electoral context and strategic party behavior have important effects on voter participation.