Why are some radical right parties included in government coalitions, while others are isolated from political cooperation through a cordon sanitaire? This book addresses this question through a study of how mainstream parties in Sweden have responded to the challenge of a radical right party: the Sweden Democrats. Sweden has been a puzzling case both in a comparative European perspective and in light of established theories of party competition. Rather than co-opting the restrictive immigration policies of the Sweden Democrats, the Swedish mainstream parties jointly converged on liberal policies. Despite their infuential position in parliament, moreover, the Sweden Democrats have been systematically excluded from government formation. This book argues that we need not invoke the idea of qualitatively diferent ‘pariah’ parties in order to make sense of such isolation of the radical right. Instead, it can be explained in terms of the strategic incentives of rival parties engaged in the pursuit of policy, office, and votes. To make this argument, the book highlights how a party’s strategic choices are constrained, between diferent levels of the party and over time. It also proposes theoretical and conceptual refinements that travel beyond the Swedish setting. The findings show that the transition from isolation to cooperation with the radical right can, under certain conditions, be a rapid process, and they challenge the perception of Sweden as a deviant case. Anders Backlund is a political scientist. This study is his doctoral thesis, completed at the Department of Political Science at Södertörn University, Sweden.