This book traces the positions of national partisan actors towards the development of the European polity in an in-depth comparative analysis covering all member states of the European Union over a period of 60 years. The author examines the approach of the social democratic, radical left, liberal, Christian democratic and radical right party families, eliciting a comprehensive analysis of partisan positions on European integration. Demonstrating that attitudes and programmatic changes towards European integration must be understood both as the product of long-term ideological traditions and domestic opposition or incumbency-seeking strategies, this book examines how far common ideological traditions lead to the emergence of convergent European policies. Based on an interdisciplinary approach that encompasses political science, history and area studies, this book provides background and analysis, and develops theory in an open and accessible style that expands the understanding of party behaviour. Using party programmes and quantitative data, the book reveals considerable cross-family variations regarding the extent to which parties’ genetic origins shape partisan responses to Europe. The Impact of European Integration on Political Parties will be of interest to students and scholars of European politics, European integration, comparative politics and political parties.