This monograph makes a major new contribution to the historiography of criminal justice in England and Wales by focusing on the intersection of the history of law and crime with medical history. It does this through the lens provided by one group of historical actors, medical professionals who gave evidence in criminal proceedings. They are the means of illuminating the developing methods and personnel associated with investigating and prosecuting crime in the eighteenth and nineteenth centuries, when two linchpins of modern society, centralised policing and the adversarial criminal trial, emerged and matured. The book is devoted to two central questions: what did medical practitioners contribute to the investigation of serious violent crime in the period 1700 to 1914, and what impact did this have on the process of criminal justice? Drawing on the details of 2,600 cases of infanticide, murder and rape which occurred in central England, Wales and London, the book offers a comparative long-term perspective on medico-legal practice –  that is, what doctors actually did when they were faced with a body that had become the object of a criminal investigation. It argues that medico-legal work developed in tandem with and was shaped by the needs of two evolving processes: pre-trial investigative procedures dominated successively by coroners, magistrates and the police; and criminal trials in which lawyers moved from the periphery to the centre of courtroom proceedings. In bringing together for the first time four groups of specialists – doctors, coroners, lawyers and police officers – this study offers a new interpretation of the processes that shaped the modern criminal justice system.