It is widely assumed that a representative democracy requires an enlightened citizenry in order to function properly. The competence of citizens has been studied extensively and the sociodemographic determinants of political sophistication are particularly well known. Much less is known about whether and how citizen competence affects electoral behaviour and outcomes. This article reviews the existing literature on these topics. Despite the widespread consensus that, generally speaking, citizen competence matters for electoral outcomes, the review produced a mixed result: some studies suggest that the political left would benefit from a better-informed electorate, while other studies suggest the opposite. Although the majoritarian electoral context is overrepresented in the evidence, the review shows that at the individual level, political knowledge greatly increases a person’s ability to match personal preferences with the right candidate or party in an election. The article also identifies several gaps in existing knowledge, thereby suggesting future research questions.