In this report we ask what the rationale is for state interventions in public behaviour and what principles should guide public policy when the state seeks to act. The report develops a framework setting out when and how government intervention in public behaviour is justified. It brings together insights from different policy areas but focuses in particular on three examples: anti-social behaviour, climate change and personal finance, specifically, people's ability to manage their finances.It considers whether government policies in these areas are appropriate and how effective they are in meeting their stated aims.