Overall, the Nordic populist radical right (PRR) parties now connect more transnationally than they did some decades ago. They have emerged as institutionalized and relevant political actors within their party systems and – except for the Norwegian Progress Party – increasingly interact bilaterally as well as multilaterally within the Nordic Council and the EU. Based on unique data from autobiographies of current and previous party leaders, interviews with key party politicians and officials, as well as a complete set of party magazines published since the late 1990s, the chapter explores whether the process of parties becoming more institutionalized and influential has been facilitated by the transnational linkages. More specifically, the chapter investigates whether a PRR party in one country has contributed to the success of a PRR party in another country by (a) providing economic and human resources; (b) serving as a role model in terms of ideology, organization, and strategy; and/or (c) facilitating processes of becoming an acceptable party. The chapter finds that there are both direct and indirect cross-national diffusion effects in relation to these three aspects.