Governments face increasingly complex, dynamic and ‘wicked’ challenges that require new policy solutions. To help them understand and respond to these challenges, policy makers often rely on evidence from advisory bodies operating at arms' length from government. This report provides a comparative overview and analysis of the important role played by these bodies in public consultation and decision making. It is based on a survey of policy advisory systems in 17 countries and a series of qualitative interviews. The report examines the institutional set up of such systems, and the role they play in the policy cycle. It discusses how to ensure that they contribute to open, inclusive and sound policy making.