For scientists seeking to play a positive role in policy and politics and contribute to the sustainability of the scientific enterprise, scientists have choices in what role they play. This book is about understanding this choice. Rather than prescribing what course of action each scientist ought to take, the book aims to identify a range of options. Using examples from a range of scientific controversies, The Honest Broker challenges us all - scientists, politicians and citizens - to think carefully about how best science can contribute to policy-making and a healthy democracy.