This book presents a comprehensive analysis of a remarkable and unexpected outcome of the 2014 referendum on Scottish independence. Despite defeat in the Scottish referendum, the two leading parties in the Yes campaign – the Scottish National Party and Scottish Green Party – experienced an extraordinary surge in membership. The book explains these events, examining the relationship between political parties and social movements, and it assesses the long-term consequences of the surge. Based on surveys of members and interviews with party and movement actors since the referendum, the book analyses the members’ involvement in the 2014 referendum, their motives for joining a party, their backgrounds and political attitudes, and their behaviour as party members. A key component of the book is how the surge changed the parties – socio-demographically, ideologically and organisationally. This book will appeal to scholars, students and observers of electoral politics, political participation, social and political movements, and political parties and their members, and more broadly to those interested in the debate on Scottish independence, British politics and comparative politics. The Open Access version of this book, available at www.taylorfrancis.com, has been made available under a Creative Commons Attribution (CC-BY) 4.0 license.