Radical right parties have changed the political landscape throughout Europe. These parties are challenging the very idea of a modern and liberal European continent. Scholars, and society as a whole, have tried to understand the success of this party family for decades. In this dissertation I argue that we need to analyze not only the number of votes radical right parties receive on election day in order to assess their success. In addition to electoral performance, success of the radical right is in this dissertation defined as sympathy among voters, policy impact and representational ability. In addition to adopting a broader definition of what determines success I argue that mainstream parties play a vital role in shaping the trajectory of radical right parties. Following this notion, an overarching argument in this dissertation is that the interaction between the radical right and mainstream parties is vital to take into consideration order to understand and explain the success of the former. This interaction, and how it shapes radical right success, is studied in different ways in the four articles. The first study looks at how mainstream party signaling affects voter sympathy towards the Sweden Democrats. By using an experimental design, the results suggest that when mainstream parties signal that they are willing to cooperate with a radical right party they challenge societal norms thus making people more likely to sympathize with the radical right party. The second study focuses on if and how mainstream parties facilitate the radical right through their positioning on the issue most closely related to the radical right, immigration. This study finds that mainstream right parties play a key role in this interaction. When mainstream right parties support a stricter immigration policy, voters are more likely to support the radical right. The third article studies the policy impact of the radical right. By studying municipal refugee reception in Sweden this article finds that radical right parties have impacted policy both directly and indirectly. The fourth study is concerned with the role of radical right parties in our representative democracy. This article finds that voters who support the radical right are poorly represented by mainstream parties, in terms of opinion congruence. Radical right parties, on the other hand, are only more congruent with these voters on the issue of immigration. In sum, this dissertation shows that if we truly want to understand the success of the radical right, we have to incorporate the mainstream in the analysis.