This research analyses the mediational role of threat perception in the relationship between prejudice and discrimination (opposition to immigration and opposition to naturalization of immigrants). In the first study, using representative samples in 21 European countries (N ¼ 36 566) from European Social Survey (2002), we showed that the relationship between prejudice and opposition to immigration was more strongly mediated by realistic than by symbolic threat perceptions. In Study 2, using representative samples in two countries with different traditions of immigration (Switzerland, N ¼ 940; Portugal, N ¼ 1514), we showed that realistic threat more strongly mediated the relationship between prejudice and opposition to immigration, while only symbolic threat perception mediated the link between prejudice and opposition to naturalization. The theoretical implications of considering threat perceptions as factors that legitimize discrimination are discussed. Copyright # 2009 John Wiley & Sons, Ltd.Research on the relationship between prejudice and discrimination (e.g. Lord, Lepper, & Mackie, 1984;McConahay, 1983;Smith & Dixon, 1968;Weitz, 1972) has been carried out within the more general framework of the early studies on the connection between attitude and behaviour (e.g. Kutner, Wilkins, & Yarrow, 1952;LaPiere, 1934;Wicker, 1969). While the literature on the relationship between attitude and behaviour specifies when attitudes predict behaviour (e.g. Fishbein & Ajzen, 1975;Zanna, Olson, & Fazio, 1980) and presents some hypotheses on how this process occurs (e.g. Fazio, 1990;Snyder, 1982; for a review, see Eagly & Chaiken, 1998), the literature on the prejudice-discrimination link still reveals some shortcomings in these matters (see Fiske, 1998Fiske, , 2000, for a review). In fact, the few studies concerning the when question have shown that the prejudice-discrimination correlation has a moderate magnitude (Dovidio, Brigham, Johnson, & Gaertner, 1996), and that this correlation depends on several moderators (Schutz & Six, 1996). To our knowledge, only the model proposed by Pereira, Vala, and Leyens (2009) has addressed the how question, predicting that the psychological processes through which preconceived attitudes lead to discriminatory behaviour involve justifying factors, such as threat perception. In fact, Pereira et al. experimentally showed that symbolic threat perception mediates the relationship between infra-humanization of Turkish people and the opposition to the adhesion of Turkey to the European Union (EU). The current paper extends Pereira et al.'s findings by testing whether distinct types of threats differentially mediate the relationship between prejudice and discrimination. Specifically, we tested the hypothesis that the relationship between prejudice and opposition to immigration in Europe is more strongly mediated by realistic threat (Studies 1 and 2) and that the relationship between prejudice and opposition to naturalization is more strongly mediated by symbolic threat (Study 2).Europe...