Once considered a relic of the past which was doomed to disappear in affluent societies, Radical Left Parties were able to survive unprecedented electoral crises in the 1980s and 1990s to become a stable and significant feature of contemporary West European politics. Despite this, our knowledge of the electorate of contemporary Radical Left parties is extremely limited. To fill this gap, this book analyzes the radical left electorate in 17 West European countries (Belgium, Cyprus, Denmark, Finland, France, Greece, Germany, Iceland, Ireland, Italy, Luxembourg, the Netherlands, Norway, Portugal, Spain, Sweden, and Switzerland) for a period of 18 years (2000–18). The research combines data from multiple sources (surveys, country-level data, and party-level data) to show how, amidst social and political change, Radical Left Parties have been able to maintain a relatively sizeable and clearly identifiable electorate with fairly similar socio-demographic and attitudinal features. Moreover, the book argues that in order to explain electoral support for Radical Left Parties it is important to consider not only voter characteristics but also the characteristics of the parties themselves and of the political and economic context in which they compete for votes. This book will be of interest to scholars of comparative politics, political sociology, electoral behaviour, and political parties.