This book provides a comprehensive analysis of how the parties of Lega and Rassemblement National have adjusted their ideologies over a four-decade period to adapt to the new transnational cleavage in Western Europe - the conflict between pro-EU and anti-EU sentiments. It sheds light on their ability to change ideological positions, policy stances, and adopt strategic shifts in response to the evolving political landscape. Drawing from a rich array of sources, the book challenges the perception of established radical right parties as inflexible, revealing their significant ideological adaptability. As such, it offers a richer understanding of the dynamics within the radical right party family. This book is of key interest to scholars and students of Euroscepticism, the Radical Right, party politics, and more broadly to European and comparative politics.