This dissertation studies how the media portray party leaders in terms of their character traits, and when and to what extent these mediated leadership images have electoral consequences. The research focusses on the media portrayal of party leaders to establish leader effects, instead of leader perceptions of voters, because (a) media are voters’ principal source of political information and, therefore, strongly affect voters’ perceptions of party leaders, and (b) this way the causal direction can be more firmly established. Mediated leader effects are studied in the Netherlands in the period 2006 to 2012 applying a multi-method research design, which includes a theoretical conceptualization of leadership traits, automated content analysis, manual content analysis, and panel data analysis. Based on the findings, four conclusions can be drawn. First, five leadership traits are used in Dutch political news coverage: political craftsmanship, vigorousness, integrity, communicative skills and consistency. Second, there is a gender bias in the way the media portray the leadership traits of politicians, related to the masculinity of the leadership stereotype. Third, media coverage of party leaders in terms of their leadership traits affects electoral behavior: positive leadership images in media coverage stimulate support for the leader’s party, and negative leadership images undermine support. Fourth, the impact of mediated leadership images on electoral behavior is conditional and (at least occasionally) dependent on the tone of the media coverage, the presence of an election campaign, whether the leadership image appears in newspaper coverage or television coverage, and specific voter characteristics.