Choice architecture is everywhere. Nudging has become fashionable. The EU and some Member states, including Germany, explore the possibilities of informing their regulatory policies with behavioural insights. This book provides a cutting-edge overview of a rapidly evolving field, reflecting on constitutional challenges, contested case and ethical choices. The volume emerged from a conference held at Humboldt-Universität zu Berlin in January 2015, and from discussions and a symposium on Verfassungsblog.