Examining Podemos (Spain), SYRIZA (Greece), and M5S (Italy), it highlights the differences and commonalities between them and their voters. The book reveals whether these parties were effectively able to change the status quo represented by mainstream parties and, secondly, whether they created novel organizational structures capable of “bring the people in”, that is, of re-mobilizing disenfranchised voters and of re-inventing the concept of participation within the political party. This book will be of key interest to scholars and students of party politics, representation, leadership, political elites, public opinion, populism, and more broadly to comparative politics, European studies, and contemporary European history.