What do we really know about the encounters between medicine and law, doctors and lawyers, in the criminal courts of the past? How and why did medical professionals enter the courtroom; what did they do to get there and what reception did they receive? This book will situate doctors in their rightful place as contributors to the investigation of crime, as part of a criminal justice system that evolved over the course of the eighteenth and nineteenth centuries to create the regularised policing and legal structures so familiar today. This chapter introduces the book and its argument in relation to the existing historiography of law, crime and policing; describes the primary sources and methodology and explains where medical professionals fit into criminal justice procedures.