This book examines how social democratic parties have responded to populist radical right parties in the battle for support from working-class voters.It focuses on the paradigmatic examples of social democratic parties in the Nordic countries. Historically these have been the strongest social democratic parties, but they have declined in recent years partly due to the competition from populist radical right parties. In addition, since populist radical right parties tend to support liberal and conservative parties in parliament or in governmental negotiations, social democratic parties’ ability to impact broader policy areas has declined as well. The book provides a detailed empirical account of how social democratic parties – and more broadly, labour movement organisations, including unions – have responded to these challenges across Denmark, Sweden, Finland, and Norway.This volume will be of interest to scholars of party politics, comparative politics, Nordic politics, and the populist radical right.