Book excerpt: France experienced an unprecedented wave of terrorist attacks in 2015. Following these tragic events, social science researchers felt the need to undertake new work to better understand the dynamics of this new radicalism. This book is the result of one of these attempts. A large quantitative and qualitative survey was conducted among French Lycée students in order to gather substantive information and propose an interpretation of the penetration of radical ideas, be they religious or political, among them. How widespread are these radical ideas? What are the main characteristics of youngsters who share them? Are there links between religious radicalism and political radicalism? How do young people feel about the 2015 terrorist attacks? How do young people use media and social media to keep abreast of and understand radical acts and opinions? Those are the main questions explored in this book. Contributors are: Vincenzo Cicchelli, Alexandra Frénod, Olivier Galland, Laurent Lardeux, Anne Muxel, Jean-François Mignot and Sylvie Octobre.