One of the fundamental roles of democratic institutions is to provide incentives to politicians to perform. Somewhat surprisingly, the literature has mostly left the role of political parties to the sidelines. We develop a model in which parties provide incentives to candidates through their candidate selection process and analyse policy outcomes across the world's two most frequent electoral rules, plurality rule and proportional representation. We show that proportional representation offers parties more room to provide incentives to their candidates than plurality rule. Our results bear fundamental implications for empirical research in comparative politics.